Kickoff in the Europa League game between Lyon and Besiktas has been delayed due to crowd trouble.
Reports had emerged of fans clashing outside the Parc Olympique Lyonnais prior to Thursday's quarter-final first leg, which prompted police involvement.
Supporters then began fighting in the stadium as both sets of players were warming up, with projectiles and fireworks launched from the upper stands forcing fans to take refuge on the pitch.
UEFA's head communications Pedro Pinto confirmed that the fixture - scheduled to begin at 8:05pm BST - would be delayed, with the game eventually kicking off at 8:51pm BST.
It is the third incident at a UEFA competition this week, following Tuesday's bomb attack on Borussia Dortmund's team bus and Wednesday's clashes between Leicester City supporters and police in Madrid.