The Ulster fan allegedly assaulted by Toulouse lock Trevor Brennan has denied provoking the player by insulting his mother.

Former Ireland international Brennan faces a lengthy suspension and possible heavy fine following the incident, which occurred during Sunday's Heineken Cup clash between the sides at Stade Ernest Wallon.

The 33-year-old climbed into the crowd and had an altercation with Ulster fan Patrick Bamford, originally from Belfast but who now lives in London.

Brennan claims he regrets the incident but insists Ulster fan Bamford taunted him about his mother.

This has been "categorically'' denied by Mr Bamford, who claims to have suffered a suspected fractured skull in the incident.

"I cannot accept that any circumstances can justify his violence,'' he said in a statement.

"There has been an attempt to justify the unexpected and still unexplained actions of Trevor Brennan which resulted in a serious assault on me.

"I categorically deny that at any point that I or anyone sitting around me was involved in sectarian abuse or in abuse of Mr Brennan about his mother.

"This recollection of events has been supported by witness statements taken at the time.''

Ulster also rubbished suggestions sectarian taunts had been aimed at Brennan, saying in a statement: "Ulster Rugby strongly refutes accusations made on RTE Radio (on Monday) regarding the use of sectarian language directed at Trevor Brennan by Ulster supporters, and is hugely disappointed that this is being used in some quarters to excuse Brennan's assault on Patrick Bamford.

"Ulster Rugby is entirely confident that the dialogue directed at Brennan was never of a sectarian nature, and will be furnishing witness statements to that effect.''

Tournament organisers European Rugby Cup have opened an investigation, led by disciplinary officer Roger O'Connor, into the incident, with 13 times-capped Brennan likely to face a misconduct complaint.

Ulster have condemned his behaviour and called for "immediate action'' to be taken by Toulouse and ERC.

"The disgraceful incident occurred when Brennan, who was warming up in front of a section of the Ulster travelling support, which included women and young families, left the playing enclosure, climbed over the pitch hoarding and physically assaulted a member of the Ulster travelling support,'' said Ulster.

"Ulster Rugby condemns Brennan for his actions, which have tarnished the game of rugby football.''

Toulouse issued a robust defence of their player - and called for ERC to investigate the behaviour of some Ulster supporters - which Mr Bamford believes "only serve to send out a very negative message about the standards of behaviour acceptable among its players''.

Brennan has also given his version of events, saying in a statement: "When I was warming up, I heard a group of supporters sing, `Brennan, your mother is a *****'.

"One of them looked me in the eyes, and again started to sing, `Brennan, your mother....'

"I then climbed the wall and had an altercation with this person. I regret this incident. But I didn't initiate it. That is the last thing I wished to do.

"I have always respected, and I have always been respected by, opposition supporters.

"I have often played against Ulster and not had these problems. I met their supporters days earlier, and it was a true pleasure.

"I love rugby, I love Toulouse and the supporters, but I love my family and my mother more than all that.''

O'Connor, meanwhile, has contacted Toulouse and Ulster, in addition to requesting reports from match officials and broadcasters at the game.