Liverpool will bid to extend their winning Champions League start and retain top spot on Tuesday when they take on holders Real Madrid at Anfield.
Manchester City hope to snap their five-game losing run in all competitions and Aston Villa aim for their first win in seven.
Here, the PA news agency takes a look at some of the main talking points before matchweek five in the competition.
Salah future hogs headlines
Liverpool, eight points clear at the top of the Premier League, are the only side to win their first four matches in this season’s revamped Champions League, but face their biggest test yet against reigning champions Real Madrid.
The build-up will be dominated by questions over Mohamed Salah’s future after the in-form Egypt striker revealed he has yet to receive a new contract offer from the club, with Trent Alexander-Arnold and Virgil van Dijk’s current deals also set to expire at the end of the season.
Sombre City must fix it
Manchester City’s barely-believable losing run brings Tuesday’s match against Feyenoord at the Etihad Stadium into sharper focus.
The Premier League champions lost five successive games for the first time since 2006 at the weekend, thumped 4-0 at home by Tottenham two days after Pep Guardiola had signed a new two-year contract.
City had a bad day in Lisbon in their previous Champions League match, losing 4-1, so can they halt the longest losing run of Guardiola’s managerial career?
Another Villa thriller?
Aston Villa have wobbled after an impressive start to life back in Europe’s premier football competition for the first time in 41 years.
Unai Emery’s side were joint top after opening with three straight wins – including a 1-0 defeat of Bayern Munich – but since beating Bologna in October they are winless in six matches and had to come from behind against Crystal Palace at Villa Park on Saturday to avoid a fifth straight defeat in all competitions.
They will bid to retain their place in the top eight against Juventus at home on Wednesday.
Gunners reignite in time
Arsenal are another team who have struggled to produce their best form in recent weeks and they face a tough task at Sporting, who ambushed Guardiola’s City 4-1 in their previous Champions League match – Ruben Amorim’s final home game in charge of the Portuguese side before heading to Old Trafford.
The Gunners sealed their first win in four games against Nottingham Forest on Saturday and aim to make it three Champions League wins from five this season in order to stay in touch with the top eight.
Celtic on a roll
Celtic moved three points clear of Aberdeen at the top of the Scottish Premiership at the weekend and head into their home match against Brugge after making it six straight wins in all competitions by beating Hearts 4-1 at Tynecastle.
Brendan Rodgers’ side sit comfortably in mid-table in the Champions League having recovered from a 7-1 thrashing by Borussia Dortmund in October.
The Parkhead faithful will relish the visit of Club Brugge on Wednesday after home victories over Slovan Bratislava and Leipzig.
