Arsenal manager Arsene Wenger could face another touchline ban after being charged over his conduct at the end of their Champions League tie with AC Milan at Emirates Stadium.
Wenger approached the officials on the field having been left incensed by the 21 fouls given against his team, and it is reported that he then confronted Slovenian referee Damir Skomina in the tunnel.
It is the third time Wenger has faced a UEFA charge in the past year. First he was banned for two matches for his comments following last year's exit at the hands of eventual champions Barcelona. The suspension was repeated after he was accused of using a coach to communicate with his players when banned for the qualifying play-off first leg against Udinese.
A UEFA spokesman confirmed: "A disciplinary case has been opened for improper conduct.''
If Wenger is banned he will be absent for the bench for Arsenal's next games in Europe.
Asked about the officials in his post-match press conference, Wenger said: "I was not happy with the referee tonight because I felt he gave many free-kicks in the middle of the park. Every time they went down a free-kick was given for them, and they sensed that very quickly and they used it very well."
The Gunners boss was also unhappy with the state of the pitch during the first leg, with the flanks at the San Siro having been relaid just days before.
"It is maybe an easy excuse, but I feel UEFA has a lot to answer for because if you arrive at 7.46pm you get fined, but you can play on a bad pitch and they don't say a word," Wenger said. "I just feel it is part of the respect for people who pay their money and go to a football game and expect conditions where you can play football. That's what we try to do here and it is unacceptable for UEFA to accept pitches like the one in Milan."
At the Emirates, Arsenal were able to exploit the space out wide to cause endless problems for the visitors in the first half. Laurent Koscielny headed home an early corner before Tomas Rosicky slotted home when Thiago Silva failed to deal with a Theo Walcott cross, and Robin Van Persie made it 3-0 with a penalty just before the break after Alex Oxlade-Chamberlain was bundled over.
Wenger was at least able to draw comfort from the performance of his team. "The players put in a faultless performance, with fantastic spirit and you can only congratulate the whole team," he said. "We were very close."
It could have been even better for Arsenal had Van Persie converted a gilt-edged chance in the second half when Christian Abbiati deflected a Gervinho shot into his path.
The Dutchman attempted a chip, which Abbiati was able to claw away, but the striker said after the match that he did not regret going for finesse over power.
"The way I saw it, the 'keeper was quite close to me so the option wasn't there to pass it left or right of him," Van Persie told Sky Sports. "I had to go for the chip. I'll have to watch back, but that's how I felt."