Organisers of the Heineken Cup, European Rugby Cup (ERC), have today opened an investigation into the off-field incident involving Toulouse players, including Trevor Brennan, and Ulster supporters.
The incident took place during yesterday's Pool Six clash at Stade Ernest Wallon between the French side and the Irish province; both of whom are former European champions.
ERC appointed their Disciplinary Officer Roger O'Connor to investigate and he has contacted both clubs, asking them to supply full details of the incident. O'Connor has also requested reports from the match officials and broadcasters at the game.
A decision on any misconduct complaints to be brought against players or the clubs involved will be made following this investigation.
Brennan, who is expected to retire at the end of the season, was seen climbing into the crowd and appeared to have singled out an Ulster fan and landed a number of punches before leaving, drenched by water thrown by the fans.
Brennan runs a popular bar, the De Danú, in Toulouse, which was full of Ulster fans on Friday and Saturday night.
According to observers, Toulouse were being baited by visiting fans after Ulster drew level 13-13 with a disputed Paddy Wallace penalty. It seems the abuse, much of it personal, was directed at Brennan.
A dozen security men moved to the area, but that did not stop Brennan's team-mate Gareth Thomas of Wales from also remonstrating with the crowd.
Ulster Rugby had reported the incident to ERC earlier today, alleging there was an altercation involving Brennan and an Ulster fan.
A statement on the club's official website, www.ulsterrugby.com read: "Ulster Rugby has made the organisers of the Heineken Cup, the ERC, aware of an off-the-field incident involving the Toulouse player Trevor Brennan.
Ten minutes after the fracas Brennan, who went on as a replacement, was shown a yellow card after scuffling with Ulster's Australian captain, Justin Harrison.
That on-field incident lasted more than a minute despite constant whistle-blowing by the Bath referee Tony Spreadbury and attempts by team-mates to separate the pair. It then resumed on the touchline as they went to the sinbin.
The inquiry hopes to rely on what, if any, footage is available from Canal+, who were broadcasting the game.
If Brennan is found guilty of the alleged assault he faces a lengthy ban which could effectively bring an unsavoury end to his career.