Manchester City secured the goalless draw they needed to edge out Atletico Madrid and advance to the Champions League semi-finals on Wednesday but the match was marred by a mass brawl late in the game that continued to rage in the tunnel after full-time.
Police were seen in the tunnel at the Wanda Metropolitano as video footage showed heated arguments breaking out between the players, including Atletico's Stefan Savic and City's Jack Grealish, with staff trying to keep the players apart, reported AFP.
"I didn't see it," said Diego Simeone. "I was on the pitch applauding the fans. By the time I went inside there was nobody there."
Pep Guardiola was asked about the behavior of Atletico's players. "Nothing to say," he said.
The trouble began on the pitch, as Atletico defender Felipe sparked a huge brawl in the corner after a taking a wild swipe at City's Phil Foden.
Felipe was sent off but not before a crowd of players, substitutes and staff swarmed in.
"We knew it was not an easy place to come, it is a hostile environment, it was a difficult night all round and how we defended and controlled ourselves over the two legs was incredible," City defender John Stones told BT Sport.
In the end, Kevin De Bruyne's first-leg strike last week at the Etihad Stadium proved enough for City to claim a 1-0 victory on aggregate in Madrid, although the Belgian had to go off with an injury which, if significant, would be a hammer blow to their hopes of winning the treble.
Kyle Walker also hobbled off in the second half.
City will now face Real Madrid, with Liverpool up against Villarreal in the other semi-final to complete an all Spanish-English line-up in the last four.
Simeone was widely criticized for Atletico's negative tactics in the first leg and there was only a minor shift here, with the plan still to keep the game tight ahead of a final push.
Atletico came close, spurning a number of late chances, but instead City advance to the semis for a second consecutive year, in sight again of their first Champions League triumph.
"If we play like we did in the second half we have no chance," said Guardiola. "We are playing Real Madrid, the kings of this competition. We will have to suffer."
After a rousing ceremony before kick-off that saw the words "Pride, Passion, Feeling" spelt out across the crowd, Atletico made a stirring start, harrying City high up the pitch and snapping at their heels in midfield.
Foden was clattered by Felipe, Stefan Savic bulldozed Ilkay Gundogan over and Walker poked a ball out of play, under stress from the Atletico press.
But City survived the early, physical onslaught and established control, even if Atletico looked a threat on the break, failing only with their final pass.
- Gundogan hits post -
City's possession should have told midway through the half when a wonderful Riyad Mahrez pass released Walker, whose cross evaded the sliding Atletico defenders and found Foden at the back post.
He teed up Gundogan for what looked a simple finish but the ball cannoned back off the post. In the scramble, Gundogan's headed rebound was blocked by Felipe.
Atletico, though, surged again after the restart, the crowd coming with them. Antoine Griezmann dipped a volley just wide of the post, Ederson lashed a nervy punt downfield and Marcos Llorente barged the ball off Joao Cancelo. Guardiola flapped on the sideline, trying to jolt his team back into life.
With 25 minutes left, De Bruyne was replaced by Raheem Sterling and soon after Simeone decided it was time to attack, Angel Correa, Yannick Carrasco and Rodrigo de Paul all coming on.
De Paul's first touch was to fire just past the post and City were retreating now, camped in their own half, accepting or unable to prevent the Atletico pressure.
Simeone rolled the dice, Luis Suarez and Matheus Cunha thrown on for the last eight minutes.
In the 86th minute, Correa chested down for Cunha but his finish was blocked by the left leg of Stones. From the corner, Ederson failed to clear and the goal was gaping but Savic was unable to steer in.
A feisty contest erupted at the end when Foden was taken out again by Felipe, who swung his leg at the City midfielder on his way down. A swarm of players, substitutes and staff rushed in and it was only a few minutes later that Felipe was sent off.
With nine minutes of added time, Gundogan should have settled it for City but Atleti survived. De Paul tested Ederson with a free-kick, the Brazilian then parrying away as Correa had the last shot.