Celtic FC, Paris Saint-Germain FC and Manchester United FC are on song but it has been harder going for Juventus and Real Madrid CF. UEFA.com surveys the returnees' form.
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It is 68 days since the group stage concluded and as well as tinkering with their squads, the eight teams that return to the UEFA Champions League this week approach the round of 16 in contrasting shape.
It all looks rosy for Celtic FC, Paris Saint-Germain FC and Manchester United FC, as it was for Borussia Dortmund before a heavy weekend defeat. Valencia CF are heading in the right direction with a new man at the helm but it has been harder going for Juventus and Real Madrid CF. FC Shakhtar Donetsk, in the middle of their winter break, provide something of an unknown quantity.
Neil Lennon's side have been in fine form since matchday six, a run of 11 wins in 13 games in all competitions helping them increase their lead atop the Scottish Premier League from a solitary point at the end of November to 18 following Saturday's 3-1 victory at second-placed Inverness Caledonian Thistle FC. Celtic have also negotiated their passage to the Scottish Cup quarter-finals, where a Saint Mirren FC team that stunned them on 27 January in the last four of the League Cup – a rare blip – await.
Juventus ended 2012 on a six-match winning run but have struggled to find their stride since the winter break, Antonio Conte's side kicking off the new year with a 2-1 home defeat by ten-man UC Sampdoria. A sequence of four victories in nine outings has seen their Coppa Italia ambitions ended by S.S. Lazio in the semi-finals and their Serie A lead cut to five points; it was eight at the turn of the year. The dip has coincided with the absence of Giorgio Chiellini, who has not played since tearing his calf in mid-December.
When Ernesto Valverde assumed the reins in early December, Valencia were 12th in the Liga, with 18 points from 14 Liga games – their worst start to a season since 1999/2000. A change in fortunes has seen them rise to fifth, though Real Madrid CF ended their Copa del Rey ambitions at the quarter-final stage amid a spell of three meetings in eight days between the sides. In the second of that trilogy, on 20 January, Madrid consigned Valencia to a 5-0 defeat at Mestalla – their heaviest ever home Liga loss.
Paris Saint-Germain FC
The French club have been irresistable since rounding off the group stage with a 2-1 victory over FC Porto. They have since won ten out of 11, drawing the other, a return that has lifted them from fourth to first in Ligue 1 and seen them through to the last 16 of the French Cup. Salvatore Sirigu, who was rested for the two cup games, went a club record 860 minutes without conceding between Jackson Martínez's consolation for Porto and Wahbi Khazri's stunning free-kick in Friday's 3-1 victory over SC Bastia.
Real Madrid CF
Madrid have won just seven of their 14 games since matchday six, losing further ground on Club Atlético de Madrid and FC Barcelona in the Liga and leading to Jose Mourinho conceding the title. "It is impossible now, there's too big a gap," he said. "We have to focus on other goals like the Copa del Rey and the Champions League." Madrid, shorn of Iker Casillas since he broke his left thumb on 23 January, are all-square at 1-1 in their Copa del Rey semi-final tie against Barcelona ahead of the second leg at the Camp Nou on 26 February.
Manchester United FC
Despite continued problems converting penalties – they have managed just four out of nine this term, Sir Alex Ferguson's team are 13 games unbeaten since rounding off the group stage with a 1-0 loss to CFR 1907 Cluj, winning ten. During that time they have stretched their lead at the Premier League summit from three points to 12 and booked a place in the FA Cup fifth round. United picked up 65 points in their first 26 top-flight games this season, their best ever return in the Premier League era (since 1992/93).
FC Shakhtar Donetsk
Shakhtar are in the middle of their three-month domestic winter break, which started at the end of November and finishes on 1 March when they host FC Volyn Lutsk. They have been in supreme friendly form, though, triumphing in ten of their 12 games and winning tournaments in Abu Dhabi, United Arab Emirates and La Manga, Spain. They did lose their most recent game, though, going down 1-0 to Norway's Odd Grenland on 3 February.
With Robert Lewandowski prolific, Dortmund were on a five-match winning run in all competitions before Saturday's 4-1 defeat at home to Hamburger SV – their heaviest loss since going down 5-1 at home to FC Bayern München on 12 September 2009. A 3-2 victory at Bayer 04 Leverkusen on 3 February allowed them to leapfrog their opponents into second spot in the Bundesliga but Bayern, unbeaten since October, remain well clear. Dortmund spent time at La Manga during their month-long winter break.