Matchday three pits Group D's top team Barcelona against the bottom side Olympiacos, with home coach Ernesto Valverde facing a club where he has had two spells in charge.
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It is top against bottom on matchday three when FC Barcelona welcome Olympiacos FC to the Camp Nou with six points already separating the sides in Group D.
• While Ernesto Valverde's current team have won their first two games, scoring four goals and conceding none, Olympiacos are still without a point and could have their work cut out to get off the mark in their first encounter with Barcelona.
• The match pits Valverde against one of his former clubs, the Barcelona coach having won three league titles in two spells at Olympiacos.
• The Blaugrana have won nine of their 12 fixtures against Greek opponents, losing two. They have won all six home games, scoring 26 goals and conceding three.
• Barça have won their last three matches against teams from Greece, all against Panathinaikos FC, including home (5-1) and away (3-0) victories in the 2010/11 group stage. Lionel Messi got three of those goals and was also on target in the 5-0 thrashing of the Greens in 2005/06.
• The Spanish side are unbeaten in their last seven meetings with Greek opposition, home and away, winning six.
• This is Barcelona's record-equalling 22nd UEFA Champions League group stage campaign, and 14th in succession. They last failed to reach the last 16 in 2000/01, although they did not take part in 2003/04.
• The Blaugrana last failed to progress beyond the round of 16 in 2006/07; their last two campaigns have been ended in the quarter-finals, by Juventus last season and by Club Atlético de Madrid in 2015/16.
• The 0-0 draw with Juve in last term's quarter-final second leg was the only time former Barcelona coach Luis Enrique failed to win a home game in the UEFA Champions League, having previously mustered 15 straight victories.
• Barcelona are unbeaten in 22 matches at home in the competition, a run that started in September 2013 (W20 D2); they were 3-0 victors against Juventus on matchday one.
• The Thrylos have never won in Spain, where their record reads W0 D2 L12.
• They have been beaten on their last five trips to Liga teams, most recently going down 4-0 at Atlético in the 2014/15 group stage; they last avoided defeat in Spain when holding RC Deportivo La Coruña 0-0 in the 2004/05 UEFA Champions League group stage.
• Olympiacos succumbed 2-0 at Juventus on matchday two, but have won three of their last five European away games, including the first two this season. In their last UEFA Champions League group campaign, in 2015/16, they won two of their three away fixtures.
• Olympiacos opened this season with a 5-3 aggregate success over FK Partizan in the third qualifying round (3-1 away, 2-2 home). They then got the better of HNK Rijeka in the play-offs, coming through 2-1 at home and 1-0 away.
• Olympiacos are in the group stage for an 18th time. They lost to Hapoel Beer-Sheva FC in last season's third qualifying round, the first time they had missed out on the UEFA Champions League group stage since 2010/11.
• In 2016/17, the Greek side went on to make the UEFA Europa League round of 16, falling 5-2 on aggregate to Beşiktaş JK.
• The Piraeus club earned a place in this season's qualifying rounds by lifting their 44th Greek championship in 2016/17 – their seventh in a row.
Coach and player links
• Valverde had two stints as Olympiacos head coach (2008/09 and 2010–12), leading them to three Super League titles and two Greek Cups. Assistant coach Jon Aspiazu and fitness trainer José Antonio Pozanko were with him at Olympiacos and have followed him to Barcelona.
• Alberto Botía joined the youth ranks of Barcelona aged 14, spent three years in their B side and made his sole senior appearance in the final Liga game of 2008/09, a 1-1 draw against Deportivo La Coruña.
• Botía also had stays at Sporting de Gijón (2009–12), Sevilla FC (2012/13) and Elche CF (2013/14). His record against Barça was W0 D1 L8.
• Marko Marin and Diogo Figueiras were part of Sevilla's UEFA Europa League-winning squad in 2013/14.
• Vadis Odjidja-Ofoe scored in Legia Warszawa's 3-3 draw with Real Madrid CF in last season's group stage.
• Mehdi Carcela-González is on loan at Olympiacos from Granada CF.
• Have played in Spain:
Saša Zdjelar (RCD Mallorca, 2017)
Karim Ansarifard (CA Osasuna, 2014/15)
Mehdi Carcela-González (Granada CF 2016–17)
• Has played in Greece:
Aleix Vidal (Panthrakikos FC, 2009)
• Have played together:
Nélson Semedo & Mehdi Carcela-González (SL Benfica, 2015–16)
Sergio Busquets & Alberto Botía (Barcelona B, 2007–08)
Thomas Vermaelen & Guillaume Gillet (Belgium)
• Semedo will incur a suspension with his next booking.
• Barcelona were the only team with a 100% record after seven games of the Liga season, but required a late Luis Suárez goal to salvage a 1-1 draw at Club Atlético de Madrid on Saturday.
• Messi has 17 goals in 16 outings for club and country this term.
• Messi's 44th career hat-trick earned Argentina a 3-1 victory away to Ecuador on 10 October, booking their place at the 2018 FIFA World Cup.
• Luis Suárez scored twice that same evening in Uruguay's qualification-sealing 4-2 defeat of Bolivia.
• Gerard Piqué and Jordi Alba featured in Spain's 3-0 home win against Albania on 6 October, a result that rubber-stamped their ticket to Russia. Sergio Busquets played three days later as Israel were beaten 1-0.
• Arda Turan won his 100th cap in Turkey's 3-0 home defeat by Iceland.
• André Gomes came off the bench as Portugal qualified by defeating Switzerland 2-0 in Lisbon, ruining their opponents' hitherto 100% Group B record.
• Ousmane Dembélé will miss the rest of the group stage with a hamstring injury sustained in the 2-1 comeback victory at Getafe CF on 16 September.
• Messi is among the final three nominees for the Best FIFA Men's Player 2017. The winner will be announced on 23 October.
• Messi and Suárez are on the 30-man shortlist for the Ballon d'Or, the winner of which will be revealed in December.
• The Piraeus outfit have 11 points from seven Greek Super League games – seven fewer than they had at the same stage last season.
• Olympiacos had lost their last three matches in all competitions – their worst run of form since February 2009 – prior to Saturday's 4-3 victory at Panionios GSS.
• Ben Nabouhane suffered a hip strain in the 1-0 home loss to Atromitos FC on 1 October and is expected to be sidelined until the end of the month.
• Kostas Fortounis and Panagiotis Tachtsidis started Greece's last European Qualifier, a 4-0 home victory over Gibraltar on 10 October that secured Michael Skibbe's men a play-off berth.