Keep track of the latest deals among the round of 32 contenders, with moves for Gent, Osmanlıspor, Rostov, Shakhtar Donetsk, PAOK, Celta Vigo, Schalke, Krasnodar, Beşiktaş and Anderlecht.
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- Schalke loan goalkeeper Fabian Giefer to English second-tier side Bristol City. The 26-year-old has been understudying Ralf Fährmann at Schalke and made his sole appearance this season in the UEFA Europa League loss at Salzburg in December.
- Artur Jędrzejczyk, 29, seals a return to Legia Warszawa from fellow UEFA Europa League hopefuls Krasnodar. The Poland midfielder started his professional career at Legia, and spent the second half of last season back there on loan.
- Tesfaldet Tekie is the latest arrival at Gent after joining from Norrköping on a three-and-a-half-year deal. The creative Swedish youth international midfielder, 19, aided his former club to the 2015 Swedish title.
Nigerian midfielder Raheem Lawal is loaned by Osmanlıspor to Kayserispor until the end of the season. Despite taking part in four UEFA Europa League group stage matches, the 26-year-old made just three substitute appearances in the domestic league this term.
- Goalkeeper Luca Lezzerini is loaned by Fiorentina to Serie B side Avellino. The 21 year-old has made one Viola appearance this season as a substitute against Chievo in August.
- Lyon midfielder Gueïda Fofana retires aged 25 due to persistent ankle problems. He last played in a reserve game in April.
- Central midfielder Adrien Trebel, 25, is unveiled as an Anderlecht player, making the move from Standard Liège.
- Bigrer Verstraete moves from Kortrijk to Gent with fellow midfielder Hannes Van de Bruggen going the other way. "It's very nice to sign for a big club like KAA Gent," said Belgium Under-21 player Verstrate, 22, who can play anywhere in midfield or even at left-back. The 23-year-old Van de Bruggen had been with Gent since 2004.
Congo striker Thievy Bifouma moves to Osmanlıspor from Bastia on a three-and-a-half-year contract from French outfit SC Bastia. Bifouma, 24, has also played for Espanyol, Las Palmas, West Bromwich Albion, Almería, Granada and Reims. Bifouma will link up with his compatriot Dzon Delarge.
Rostov sign 33-year-old Serbian-born Ukrainian international Marko Dević on an 18-month contract. The former Shakhtar Donetsk forward had been without a club since December's departure from Rubin Kazan.
- Tottenham Hotspur sell midfielder Tom Carroll to Swansea City. The 24-year-old youth product had made only three Spurs appearances this season.
- Argentinian forward Gustavo Blanco Leschuk moves to Shakhtar Donetsk on a three-and-a-half-year deal. The 25-year-old leaves Kaparty Lviv having previously played in Sweden, Morocco and Russia.
- Former Lyon defender Aly Cissokho, 29, joins Olympiacos on loan from Aston Villa, with the Greek side holding the option to make the move permanent in the summer.
- Former Ludogorets defender Júnior Caiçara departs Schalke for surprise Turkish league leaders İstanbul Başakşehir.
- APOEL have made forward David Barral, most recently of Granada, their first acquisition of the January window. The 33-year-old has penned an 18-month deal.
- Legia Warszawa striker Aleksandar Prijović, who scored twice in the record-breaking 8-4 loss to Borussia Dortmund on UEFA Champions League matchday five, has left the Polish club for fellow round of 32 contenders PAOK on a deal running until summer 2021.
- Erstwhile German international Sidney Sam, still only 28, departs Schalke for Darmstadt on loan for the rest of the season.
- Fiorentina have announced the signing of goalkeeper Marco Sportiello on loan from Atalanta until June 2018, with an option to make the deal permanent. The highly-rated 24-year-old will compete with Ciprian Tătărușanu for the No.1 jersey.
Celta Vigo have added to their array of impressive, technical midfielders by capturing Jozabed on loan from Fulham. Jozabed returns to Spain after a sparkling 2015/16 campaign with Rayo Vallecano in which he scored nine Liga goals.
- France midfielder Morgan Schneiderlin has been reunited with former Southampton manager Ronald Koeman at Everton. He has joined the Toffees from Manchester United on a four-and-a-half-year deal for a fee that could rise to €27.5m.
- Midfielder Nicolaj Thomsen agrees a move to København from Nantes, signing a contract until 2021 with the Danish champions. "I have great ambitions to win trophies here," said the 23-year-old, who only arrived in France during the summer.
- Sheffield Wednesday forward Sergiu Bus, who spent the first half of the season on loan at Italian side Salernitana, agrees an 18-month contract with Astra Giurgiu, where he has been signed as a replacement for the Steaua-bound Denis Alibec.
- Winger Felipe Pardo goes on loan from Olympiacos to Nantes for the rest of the season. The former club of Olympiacos strategic adviser Christian Karambeu will have the option to purchase the 26-year-old Colombian outright.
- Turkey winger Olcay Şahan, 29, leaves Beşiktaş to join Trabzonspor on a three-and-a-half-year contract. Olcay has struggled to hold down a starting place for the Black Eagles this season.
- Lyon allow 20-year-old midfielder Olivier Kemen to join Ligue 2 Gazélec Ajaccio on loan until the end of the season to gain playing time.
- Genk pick up 22-year-old striker José Naranjo from Celta Vigo on a three-and-a-half-year deal.
- Schalke have reacted to injury concerns in defence by signing Bayern München's Holger Badstuber on loan until the end of the season. Badstuber, 27, has won 31 Germany caps.
- Attacking midfielder Yohan Mollo, 27, has swapped Kryla Sovetov for Zenit, committing himself to the Saint Petersburg club until summer 2020. Mollo is the cousin of France striker André-Pierre Gignac.
- Krasnodar sign 22-year-old Ecuador left-back Cristian Ramírez from Ferencváros, tying him to a deal until summer 2021.
- Schalke snap up 2. Bundesliga top scorer Guido Burgstaller from Nürnberg subject to a medical. The Royal Blues will hope that the Austrian, 27, can help fill the void left by injuries to Breel Embolo, Klaas-Jan Huntelaar and Franco Di Santo.
- Brazilian centre-back Carlão ends two and a half years at APOEL. "I had offers from other countries, including Greece and Germany, but when I heard there was interest from Torino, I immediately said yes," says the 30-year-old.
- Gent sign striker Darko Bjedov, 27, from Serbian side Javor Ivanjica. Kalifa Coulibaly is on Africa Cup of Nations duty with Mali.
- Lyon loan 20-year-old forward Aldo Kalulu to Ligue 1 rivals Stade Rennais for the remainder of the season.
- Ludogorets have added Brazilian goalkeeper Renan dos Santos to their ranks. The 27-year-old arrives from Avaí FC in his homeland.
- Beşiktaş make their second signing of the winter, capturing Matej Mitrović, 23, in a €4.2m move from HNK Rijeka. The Croatia centre-back has agreed a three-and-a-half-year contract.
- Ludogorets raid domestic rivals Botev Plovdiv for the services of João Paulo. The Brazilian striker, 28, is the Bulgarian A League top scorer alongside new team-mate Claudiu Keșerü on 12 goals.
- Legia Warszawa bring in Daniel Chima Chukwu from Norwegian side Molde on a three-and-a-half-year contract. The Nigerian striker replaces Chicago Fire-bound Nemanja Nikolić at Legia, who have also re-signed defender Artur Jędrzejczyk from Krasnodar.
- Sparta Praha start their winter training with two new acquisitions - Spanish forward Néstor Albiach from Dukla Praha and Romanian forward Bogdan Vătăjelu from Universitatea Craiova.
- Sweden forward Isaac Kiese Thelin joins Anderlecht on loan from Bordeaux.
- Cheick Diabaté, scorer of five goals in his last four outings of 2016, departs Osmanlıspor to join Metz on loan, while Ajax's Nemanja Gudelj moves to Chinese side Tianjin.
- Denis Alibec marks his 26th birthday by starting training with Steaua București following his move from Astra Giurgiu.
- Olexandr Karavaev joins Fenerbahçe on loan from Shakhtar Donetsk. The 24-year-old has spent the past two-and-a-half seasons on loan at Zorya Luhansk, and was in the side that met Fener twice during the group stage.
- Bundesliga strugglers Borussia Mönchengladbach sign French centre-back Timothée Kolodziejczak from Sevilla on a long-term deal.
- Legia Warszawa's Poland right-back Bartosz Bereszyński joins Sampdoria.
- Roma make Iago Falque's loan move to Torino permanent while Juan Iturbe is sent the same way until the end of the season.
- Gent bring in Nigerian teen Samuel Kalu from Trenčín while Lazaros Lamprou, 19, links up with PAOK from Iraklis.
- St-Étienne loan Jonathan Bamba to Angers until the end of the season. The 20-year-old winger spent the first half of the campaign with Belgian side Sint-Truiden.
- Zenit's key midfielder Axel Witsel joins Tianjin Quanjian of the Chinese Super League.
- Wilfred Ndidi, 20, agrees a move from Genk to English champions Leicester City. The Nigerian midfielder had been ever-present for the Group F winners in the UEFA Europa League this season.
- Former Liverpool, Ajax and Netherlands striker Ryan Babel, 30, signs a two-and-a-half-year deal with Beşiktaş having been released by Deportivo La Coruña.
- Genk pull off a bit of a coup by snapping up highly-rated 18-year-old midfielder Sander Berge from Vålerenga in Norway.
- Thomas Delaney officially starts at Werder Bremen after the "best six months" of his career captaining København after his transfer to the Bundesliga was made public.
- Midfielder Uroš Matić – younger brother of Chelsea's Nemanja Matić – was announced as a new København signing from Sturm Graz back on 13 December. The club's central defender Per Nilsson, meanwhile, has retired, aged 34.