London - Nine-time winner Real Madrid faces Juventus in the third-round Champions League match that could be worthy of a final.
The Spanish giants and the Serie A champions have 11 European Cups between them, have plenty of stars, and their clash on Wednesday in the Spanish capital is expected to be a classic, though Juventus is already trailing Real by four points in Group B.
"It's a massive test for us," said Juventus coach Antonio Conte. "We're facing a club that really wants this title, because of their history and their hunt for a 10th European Cup."
Defending champion Bayern Munich is aiming to maintain its perfect record in Group D against last-place Viktoria Plzen, while Manchester United hosts Real Sociedad in Group A on the back on of another disappointing result in the Premier League.
Here are five things to know ahead of this week's matches:
WHO HELPS RONALDO?
In the previous four seasons at Real Madrid, Cristiano Ronaldo had plenty of help up front with Gonzalo Higuain and Karim Benzema. But now that Higuain is gone and both Benzema and new arrival Gareth Bale are struggling to find their form, the question hovering over Madrid is who will share the scoring burden with the Portugal forward against Juventus.
Ronaldo scored his eighth goal in nine rounds in the Spanish league to cap a 2-0 win over Malaga on Saturday, and he leads the Champions League with five this season. Youngster Alvaro Morata accompanied Ronaldo on Saturday in place of Benzema, who injured his leg in practice. Madrid coach Carlo Ancelotti said he expects Benzema to be fit in time for the Italian champions' visit.
Benzema has been jeered by the Santiago Bernabeu crowd in recent games due to his scoring drought for the club which stretches back a month. Bale played 15 minutes on Saturday after recovering from his second muscle injury already this season.
GUARDIOLA'S DEFENSIVE HEADACHE
Bayern Munich coach Pep Guardiola faces the problem of plugging a gaping hole in the center of his defense against Viktoria Plzen. German international Jerome Boateng is suspended following his red card in the 3-1 win at Manchester City and Dante injured his ankle during Saturday's 4-1 Bundesliga win at home over Mainz.
Franck Ribery was more optimistic about his chances of featuring after sitting out Saturday's game with a left ankle injury. "The foot's a little injured but it's not so bad," Ribery said.
Plzen lost 6-1 in its only previous visit to Munich, in 1971, and anything other than a third straight defeat in Group D for the Czech side would be a surprise.
WHAT'S WRONG WITH UNITED?
Is it Alex Ferguson's retirement? The lack of quality players in midfield? The loss of its fear factor? Whatever the reason, Manchester United seems to be a completely different team to the one that won its 20th Premier League title last season. United is eight points behind Arsenal in the Premier League after being held to a 1-1 home draw by Southampton and this is a wounded team that hosts Real Sociedad.
Against Southampton, United created many chances through Robin Van Persie and Wayne Rooney but did not manage to put the game away. The Red Devils' new boss insists Ferguson's departure is not linked to the current lack of killer instinct among his players.
"The fear comes from the team on the pitch," said David Moyes. "Obviously Sir Alex Ferguson has a great history and his experience will always work in charge of any team. But the players have always been the people that have to turn out and do it."
ARSENAL'S CRUCIAL GAMES
The Gunners host last-season's runnerup Borussia Dortmund this week before traveling to Germany for a double-header likely to be decisive for the final positions in a tough Group F.
"It is already a very important tie because usually (matchday) three and four usually are decisive, so that could be the key for us to qualify," Arsenal manager Arsene Wenger said after back-to-back wins over Marseille and Napoli. Borussia collected its first victory against the French side.
Arsenal's resurgence at the top level is largely due to the arrival of German playmaker Mesut Ozil, who scored twice on Saturday in a 4-1 win over Norwich.
"Signing Mesut makes a big statement," said Arsenal midfielder Mikel Arteta. "We have added to the squad. That tells you in which direction the club wants to go. It gives you great confidence when players are coming in. Psychologically, it is very different to when you see your best players leaving."
Only 400 PSG fans will travel to Brussels for Wednesday's Group C match against Anderlecht and no fans will be issued tickets if they try to travel independently amid concerns of a hooligan threat between the two teams. PSG has contacted Belgian authorities to alert them of the potential hooligan menace.
Last season, similarly, PSG warned Croatian authorities that about 100 hooligans were rumored to be travelling to the match against Dinamo Zagreb. The French Interior Ministry issued a decree banning Dinamo Zagreb fans from attending the return match - although there was fighting the night before the game between rival thugs in the Bastille area.