Real Madrid coach Carlo Ancelotti hailed his "extraordinary" players after they set a Spanish record for consecutive victories of 19 thanks to a 4-0 success at home to Ludogorets.
Holders Manchester City will take on RB Leipzig, Red Star Belgrade and Young Boys in Group G.
Liverpool's Luis Diaz scored a hat-trick as they maintained their perfect Champions League campaign with a barnstorming second-half display in a 4-0 victory over Xabi Alonso's Bayer Leverkusen at Anfield on Tuesday.
Liverpool received a relatively kind draw for the group stage of this year's Champions League
Real Madrid beat Leganes 2-1 in La Liga on Saturday after coach Zinedine Zidane heavily rotated his side in preparation for Tuesday's Champions League semi-final second leg against Bayern Munich, including leaving out top-scorer Cristiano Ronaldo.
A second half double from Karim Benzema helped Real Madrid to a 4-1 victory at Girona on Sunday and maintain their perfect La Liga start in the post-Cristiano Ronaldo era.
Undefeated since late December, Barca are the only team in Europe's top-five league who have yet to lose in 2025.
Here, Reuters Sport highlights five reasons why last season's double winners have collapsed.
Real Madrid opened a two-point lead over Villarreal at the top of La Liga when Cristiano Ronaldo set a club scoring record in a 3-0 stroll at home to Levante on Saturday.
There were a few nerves at the end but Liverpool set up a Champions League semi-final with Spain's Villarreal after Roberto Firmino scored twice in a 3-3 second-leg draw with Benfica on Wednesday to ensure a 6-4 aggregate win.
Bayern said the 30-year-old striker was signed until 2027 after protracted talks between the two clubs.
Atletico Madrid coach Diego Simeone praised his team's spirit after knocking holders Barcelona out of the Champions League.
Real went top with one game to play after thrashing Atletico Madrid 4-0 while rivals Sociedad slipped to a 3-2 defeat at Celta Vigo.
Real Madrid's stuttering season continued as they were reduced to 10 men and then slumped to an 11th La Liga defeat of the campaign by going down 3-1 at Real Sociedad.
Cristiano Ronaldo answered his critics with a hat-trick as Real Madid came from behind to win 4-1 at Alaves and provisionally go three points clear at the top of La Liga.
'This was why Juventus brought me here. To help do things that they have never done before'
Spain goalkeeper Iker Casillas left Real Madrid on Saturday after 16 seasons as an iconic figure at the Bernabeu.
Real were smarting from a surprise 1-1 draw at struggling Elche in their last match and were missing captain Sergio Ramos, who was out with a stomach bug.
Real Madrid's Javier Hernandez struck twice as they came from behind to beat Celta Vigo 4-2 away and keep the pressure on Barcelona at the top of La Liga on Sunday.
La Liga champions Barcelona stayed on the heels of leaders Real Madrid by coasting to a 3-0 home win over Athletic Bilbao on Saturday as Lionel Messi became the club's top scorer from free kicks.
Chelsea's Champions League semi-final defeat by Atletico Madrid hinged on a pivotal second-half minute and the expertise of a young goalkeeper on loan from the Premier League club to the Spanish side, Jose Mourinho said on Wednesday.
Atletico Madrid delayed Barcelona's La Liga title celebrations by beating Valencia 3-2 at home in an entertaining game on Wednesday at a sparsely attended Wanda Metropolitano stadium.
Holders Bayern Munich and nine-times winners Real Madrid will face each other in a mouthwatering Champions League semi-final this month with Atletico Madrid up against Chelsea.
Real Madrid captain Sergio Ramos performed another rescue act to wreck Napoli's brave comeback attempt and take the Champions League title-holders into the quarter-finals.
David De Gea has left Manchester United following the end of his contract after 12 seasons with the Old Trafford side.
Manchester United were mistakenly drawn with Villarreal, even though both teams faced each other in the group stage while the Premier League side's ball was not added to the bowl as a potential opponent for Atletico Madrid.
Real Madrid paid more than 200 million euros ($227.76 million) to assemble their forward line of Cristiano Ronaldo, Gareth Bale and Karim Benzema, but the attacking trio failed them again in Wednesday's Champions League exit to Juventus.
Morata to stay on loan at Juventus for another season
In his absence, the league champions have made a lacklustre start to the season, losing their opening game to Athletic Bilbao before taking just four points from fixtures against Real Betis and Osasuna.
Lionel Messi's double strike helped Barcelona scrape a 3-2 victory over Real Sociedad on Saturday to keep the pressure on La Liga leaders Real Madrid, who needed a brace from Isco to beat Sporting Gijon by the same scoreline.
The Polish striker will miss games against Espanyol, Atletico Madrid and Getafe when LaLiga resumes after the World Cup.
Atletico Madrid were handed a chance to avenge last season's Champions League final defeat by city rivals and record 10-times winners Real after the two sides were drawn together in the last eight on Friday. Paris St Germain and Barcelona were paired together having met in the group stage, with the French side winning in Paris and the Catalans coming out on top in Spain.
Diego Costa's season is getting better and better. The Atletico striker found the net again and took the Madrid team atop the La Liga table.
Cristiano Ronaldo and Lionel Messi will resume their perennial battle to be crowned the world's best footballer after they headed the shortlist of 30 players for the 2016 Ballon d'Or announced on Monday.
News of all that's transpired on and off the football field
Real Madrid saw off a stirring Chelsea fightback to book their place in the Champions League semi-finals following a 3-2 defeat after extra time in a scintillating second leg at the Santiago Bernabeu on Tuesday to go through 5-4 on aggregate.
A Neymar double, a spectacular volley from Luis Suarez and a goal for Lionel Messi saw top of the table Barcelona's unstoppable strike force sweep aside Real Sociedad 4-0 in La Liga on Saturday.
Luuk de Jong's first-half header gave Barcelona a 1-0 win at Mallorca
Real Madrid were the big winners in Spain as their success at Almeria was followed by a Barcelona draw and a surprise Atletico Madrid defeat.
News of all that's transpired on and off the football field
