Manchester United boss Sir Alex Ferguson believes Arsenal's Robin van Persie should have been sent off after he clashed with Kieran Richardson.
Ferguson accused Van Persie of elbowing the United midfielder during their 1-0 Carling Cup win at Old Trafford.
"He was lucky to stay on," he said. "It just exploded with Van Persie's behaviour just after half-time.
"I think the FA will have to take a look at that. I think he threw an elbow at the boy," added Ferguson.
Arsenal boss Arsene Wenger admitted he feared Van Persie could have been sent off.
"I did fear it was going to be worse than a yellow card, it could have
been," admitted Wenger.
"Robin shows great potential but he has to learn to keep his nerves under
control and not get over-excited.
"I considered bringing him off because he was involved in some heated
United went through to the semi-final courtesy of David Bellion's goal after just 19 seconds.
Ferguson added: "We got a good start and played very well in the first half but were complacent in the second half.
"But now we're in the semi-finals and one step away from Cardiff.
"In these types of games the important thing is to win - but we wasted a lot of great opportunities to finish it all off.
"I was looking for more in the second half - we should have been three or four up at half-time but in the second half we did not have the same type of creation.
"I think some of the players wanted to prove themselves to fans.
"Some of the fans haven't seen a lot of the likes of Chris Eagles and David Bellion and in that respect they want to do well.
"But the outstanding feature is I think that Arsenal only had one shot, from a free-kick."
Ferguson revealed he will resist the temptation to bring back some of his first-team regulars for the two-legged semi-final against Chelsea, which takes place in January.
He added: "They are one step from Cardiff and I'm going to stick with them in the semi-final - I think they deserve it."