Matchday five of the Champions League could mean qualification for the last 16 for some - and spell trouble for others.
Bayern Munich and Manchester City are already through, but their respective opponents, Atletico Madrid and Porto, could do with positive results.
Real Madrid recorded a valuable win at Inter last time out but must do better against Shakhtar Donetsk than they did on matchday one, while the Nerazzurri themselves know nothing but a victory at Borussia Monchengladbach will do.
Liverpool need just a point at home to Ajax to progress, but with injury problems mounting and a 2-0 home loss to Atalanta last week, their progress no longer looks to be such plain sailing.
Shakhtar Donetsk v Real Madrid: Zidane's men aim to qualify against goal-shy opponents
Shakhtar's 3-2 win at Madrid was a serious shock, one that became more apparent as they lost their latest two games by four or more goals without scoring. Only Malmo and Red Star Belgrade have ever done so in three consecutive matches.
Indeed, Shakhtar have failed to score with each of their 23 shots since netting their third in the Spanish capital.
Madrid know a victory will guarantee their place in the knockouts for the 24th season in a row, a competition record. Their form might be inconsistent, but they have lost only one of their previous seven away games against Ukrainian opponents – a 2-0 defeat to Dynamo Kiev – since March 1999.
Atletico Madrid v Bayern Munich: Holders could match club record – but without Lewandowski
Bayern Munich will match a club-record seven away wins in a row in the Champions League with victory at Atletico Madrid. They have won their previous six by an aggregate score of 27-7.
Diego Simeone has lost three of his five meetings with Bayern in this competition, but Atleti have only been beaten once at home in Europe in their previous 24 games.
Robert Lewandowski needs just one goal to surpass Raul in the all-time goalscoring list in the tournament, having reached 71 against Salzburg. However, with the striker missing this contest, Atleti may fancy their chances of beating Bayern at home for the third time in a row.
Borussia Monchengladbach v Inter: Can Conte fix his Champions League woes?
Since losing the first meeting in 1971, Borussia Monchengladbach have gone four games unbeaten against Inter.
This season marks the first occasion Inter have ever failed to win any of their opening four Champions League matches, and they are at risk of losing three in a row in the group stage for the first time.
Indeed, Antonio Conte has won only 20 per cent of his Champions League games in charge of the Nerazzurri, the lowest ratio of any of his predecessors over at least five games in the competition. Fail to win in Germany, and Inter are out.
Porto v Manchester City: Imperious defence meets clinical attack
Porto have lost three games in a row against Manchester City 9-2 on aggregate and are winless in five previous meetings with English opponents.
Pep Guardiola's side have already kept three clean sheets this term, one more than they managed in nine Champions League matches in 2019-20.
Porto, however, have scored with 25.8 per cent of their shots this season, a tally only bettered by Gladbach (28.6 per cent).
Liverpool v Ajax: Mane must find magic touch
Ajax and Liverpool have not met at Anfield since 1966-67, when the Eredivisie side won the tie 7-3 on aggregate. That was the last occasion the Reds lost to a Dutch side (they have played 14 such games since).
Ajax are unbeaten in 11 away games in the Champions League, their best run since March 1997, and they have not lost in their latest five visits to England in this competition.
Liverpool, who need a point to progress, could do with Sadio Mane finding form. The forward has scored only once at home in his previous 10 appearances in this tournament, going 426 minutes without finding the net in that run.
Lokomotiv Moscow v Salzburg
20 – Of the 20 shots attempted between these sides in their matchday-one meeting – which ended in a 2-2 draw - 15 of them were by Salzburg. Indeed, Lokomotiv Moscow scored twice from just three shots on target in the game.
50 – Since the start of last season, Salzburg's 10 games in the Champions League group stages have seen 50 goals scored (23 for, 27 against), the most of any club. Salzburg have won just two of those 10 games (D2 L6).
Atalanta v Midtjylland
3 – Midtjylland have lost all three of their previous games against Italian opponents in European competition, conceding 13 goals and scoring just one in reply.
1 – Atalanta have only failed to score in one of their last 12 games in the Champions League (25 goals in total), although this did come in their most recent home game in the competition, losing by five goals to Liverpool.
Marseille v Olympiacos
13 – Marseille have lost their last 13 Champions League matches – a competition record – scoring just six goals and conceding 29.
10 – The Ligue 1 side (six) and Olympiacos (eight) are the only two teams in the Champions League in 2020-21 yet to attempt at least 10 shots on target, with the Greek team managing just one across their previous two matches against Man City.