Toulouse's former Ireland international Trevor Brennan has expressed regret for coming to blows with an Ulster fan in an off-field incident at the weekend.

"I regret this incident happened, I didn't initiate or provoke it," he said in a statement to the Irish Times newspaper on Tuesday. "It was the last thing I would have wished for."

Toulouse's 28-13 victory at home in their Pool Five Heineken Cup match on Sunday was overshadowed by the altercation just after halftime when Brennan waded into the crowd and punched a spectator.

Toulouse defended the player, asking European Rugby Cup organisers to investigate the behaviour of some of the Ulster fans who, the club said, had subjected Brennan to "unendurable provocation."

Toulouse said some of them had chanted "Brennan, your mother is a whore" while he was warming up and had then sprayed beer over him when the player approached them.

"Most of the Ulster supporters showed exemplary sportsmanship and even intervened, trying to calm the group down and asking Trevor Brennan not to pay attention to what those people were saying," the club said.

"As Brennan was about to resume warming up, a member of the group provoked him and started singing again....That is when Trevor Brennan had an altercation with that person."

"Trevor Brennan is a generous player who has always respected opponents and fans," the club added. "It took a reiterated and unendurable provocation for him to react in an unacceptable but humanly understandable manner."

Ulster Rugby issued a statement condemning Brennan and urging the ERC to take immediate action against him.

The ERC said on Monday it had opened an investigation into the incident, asking for full details from both clubs as well as reports from officials and broadcasters at the game."