Arsene Wenger felt the decision to dismiss Robin van Persie cost his Arsenal side their place in Europe.
The Gunners crashed out of the UEFA Champions League on Tuesday after suffering a 3-1 defeat away at Barcelona to exit the competition 4-3 on aggregate.
They had arrived in Catalunya looking to defend, or possibly build, on a 2-1 first leg advantage, but were unable to get to grips with Barca's passing game.
A Sergio Busquets own goal handed them a lifeline early in the second half, but the game swung in favour of the hosts once Van Persie was shown a red card shortly after.
Wenger admitted at full-time that Arsenal, who failed to muster a shot on goal, had been beaten by a very good side, but he is convinced his side would have offered more had the match officials not left them a man short.
"We lost against a good team," he told Sky Sports.
"In the first half we resisted the pressure. I believe that straight away in the second half it would have been very interesting if it had stayed 11 against 11. But that was not the case and at the end of the day we have many regrets.
"We were beaten by a terrific side, certainly the best team in Europe. I am still convinced that in the second half we could have done a lot at 1-1 if it had stayed 11 against 11."
On Massimo Busacca's decision to show Van Persie a second yellow card for allegedly kicking the ball away, Wenger added: "He must never have played in games of football of that importance, with people shouting.
"Even if he takes the chance, I don't see why it was a second yellow card. He must never have played football at all to do that."
A disappointing night for Arsenal also saw Cesc Fabregas replaced after struggling throughout, while goalkeeper Wojciech Szczesny lasted less than 20 minutes before being forced off with a dislocated finger.
Wenger insists he is no position to comment on the fitness of either player right now, but Szczesny appears to be set for a lengthy spell on the sidelines.
"It's too early to say, I don't know," said the Frenchman when pressed on the problems.