He had been warming up with his fellow Toulouse substitutes just beforehand.

A statement from Toulouse stated: “Trevor Brennan is a generous man who has always respected opponents and their supporters. It required sustained and repeated provocation to make him react in an unacceptable but understandably human way.

“(Rugby is a) sport which has always placed an emphasis on the values of friendship and camaraderie. We want European Rugby Cup (ERC) to investigate the behaviour of some of the Ulster supporters.”

Brennan, a 33-year-old Dubliner, who won 13 caps for Ireland between 1998 and 2001 and played in the country’s 1999 World Cup campaign before joining Toulouse, later appeared in the game. But he was yellow-carded after exchanging blows with Ulster’s Australian lock Justin Harrison. Both players were sin-binned by English referee Tony Spreadbury, yet Ulster are likely to cite Brennan after reviewing video footage.

ERC announced their disciplinary officer Roger O’Connor will probe the off-field incident.

O’Connor has contacted Toulouse and Ulster asking them to supply full details, and he has also requested reports from the match officials and broadcasters at the game. Following his investigation, O’Connor will decide whether to lodge any misconduct complaints.

Brennan though, seems certain to be facing a lengthy suspension and possible fine. Ulster were fuming at the way events unfolded, releasing a statement on their return to Ireland.

It 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. During the match between Toulouse and Ulster in Toulouse on Sunday, Brennan left the playing enclosure and physically assaulted a member of the Ulster travelling support.

“Ulster Rugby will be submitting a formal report to assist ERC in their investigation of this serious matter. Brennan was also involved in an incident on the field of play which Ulster Rugby will be reviewing.”