English clubs return to European action this week with the start of the 2020-21 Champions League group stage.
Here, the PA news agency takes a closer look at the opposition clubs.
Sevilla: Former Spain and Real Madrid head coach Julen Lopetegui has been in charge at the Ramon Sanchez Pizjuan since June 2019.
PSG: German coach Thomas Tuchel has won successive Ligue 1 titles since replacing Unai Emery at the Parc des Princes in 2018.
Porto: The Dragons are managed by ex-Portugal winger Sergio Conceicao. The 45-year-old had two spells with the club as a player and returned as coach in June 2017.
Ajax: Two seasons ago, Erik Ten Hag led Ajax to the semi-finals of the Champions League for the first time since 1997, having succeeded the sacked Marcel Keizer in December 2017.
Sevilla: The Spanish side have limited Champions League pedigree but are the reigning Europa League holders, a competition they have won a record six times.
PSG: Having previously failed to go beyond the quarter-finals, big-spending PSG reached last season's final, losing 1-0 to Bayern Munich in August.
Porto: Jose Mourinho guided the Portuguese side to a shock triumph in 2004. Monaco were beaten 3-0 by Mourinho's men in the final in Gelsenkirchen.
Ajax: The Amsterdam club are four-time winners of the competition, most recently in 1995 under Louis Van Gaal. They have also been runners-up twice.
Sevilla: Los Rojiblancos suffered a 1-0 defeat at Andalusian rivals Granada on Saturday, their first LaLiga loss from four fixtures this season.
PSG: French champions PSG sit second in Ligue 1 on the back of five successive wins, including scoring 10 goals in their past two games. The fine form followed consecutive defeats.
Porto: The 29-time and reigning Portuguese champions have gone two games without victory. Saturday's 2-2 draw with Sporting Lisbon followed a 3-2 home loss to Maritimo.
Ajax: Ten Hag's men have taken 12 points from a possible 15. They recovered from a 1-0 loss to Groningen to thrash Heerenveen 5-1 on Sunday.
Sevilla: Tuesday's Stamford Bridge clash will be Chelsea's maiden match against the Spaniards.
PSG: Marcus Rashford's controversial late penalty sent Manchester United through to the competition's quarter-finals on away goals in 2019 on their only previous meeting with PSG. The two-legged tie finished 3-3 on aggregate.
Porto: City, under the management of Roberto Mancini, defeated Porto 6-1 on aggregate during the last 32 of the 2011-12 Europa League. Sergio Aguero scored in each leg.
Ajax: Liverpool were beaten 5-1 on their only previous trip to Ajax, part of a 7-3 aggregate loss in the second round of the 1966-67 European Cup.