Sir Alex Ferguson said Patrick Vieira, who struck Arsenal's winning kick in the FA Cup final shoot-out, could have been sent off earlier in the game.
The Manchester United manager claimed the Gunners captain had an "immunity" from referees.
Vieira was booked in extra-time but escaped another caution from Rob Styles, who sent off Jose Reyes.
Ferguson said: "Patrick seems to have an immunity to these kind of things so I'm not surprised."
He added: "These games are very difficult for referees. Where do they start or stop?
"There were a lot of fouls and I don't think there were any really bad ones, although Reyes was perhaps a bit lucky not to be sent off for his tackle on Mikael Silvestre.
"You don't want to see players sent off in the final but referees are only human beings."
Ferguson, who also accused Arsenal of being "boring", said his United side would bounce back stronger after their shoot-out defeat, which followed a 0-0 draw.
"We've always been the sort of team that is galvanised by defeat and adversity.
"We're that sort of team. We'll get ourselves off the ground, cup football can do that to you sometimes.
"We are a very good team and in that form we can play against anybody.
"It was a really good performance and we got our game together today.
"You could toss a coin for man of the match out of Wayne Rooney and Cristiano Ronaldo because they were great, the pair of them.
"There's a great future for those boys and Darren Fletcher as well.
"The season's over now and we can reflect on what might have been as long as we like but we have to look forward to next season now."
United skipper Roy Keane rued his side's hatful of missed goal opportunities.
"We played quite well and had plenty of chances but it's about putting the ball in the back of the net and we didn't quite manage it," said the Irishman.
"It's small consolation to say that we had all the chances.
"We dominated but I'm sure the Arsenal players won't be too bothered about that - they've got the winners' medals and the cup and we haven't."
Defender Rio Ferdinand was distraught after losing the match on penalties.
"It's a bit of sucker punch really," said the England international.
"You go into a cup final, you want to win. It's disappointing but I'm sure we'll come back.
"It was a very good team performance but at the end of the day if you don't score goals, you don't win games."