Arsenal boss Mikel Arteta says Spanish midfielder Dani Ceballos ignored his half time instructions during a 2-1 defeat to Villarreal.
The north Londoners have to come from behind at home in the second leg of their Europa League semi final, after losing the first leg in Spain.
Villarreal were 2-0 up after the halftime mark, before Ceballos was shown his second yellow card for a reckless tackle.
Arteta said of the red card post-game: “I haven’t seen the action again obviously we talked at half time that you have to be careful.
“I was going to take him off but by the time Gabi (Gabriel Martinelli) was ready to come on that action happened and he was out.”
Arsenal did battle back in the game through a Nicholas Pepe penalty, and can go through with a 1-0 success at home in the second leg.