Heineken Cup chiefs have opened an investigation into alleged use of abusive and racist language during a pool clash between Ulster and London Irish.

Irish contacted European Rugby Cup Limited about the matter, and ERC disciplinary officer Roger O'Connor has written to the Guinness Premiership club and Ulster requesting full details of the alleged incident by January 3rd.

O'Connor will then decide whether or not there are grounds to proceed with a misconduct complaint.

Earlier this week, Ulster mounted a vigorous defence of second-row forward Matt McCullough following allegations by Irish that he racially abused Delon Armitage.

The incident is alleged to have taken place in last Friday's encounter in Belfast, won 29-13 by Ulster.

Irish did not publicly name McCullough, and they confirmed they had received a formal apology from an Ulster player for what they described as "foul and abusive language".

But Ulster chief executive Michael Reid stressed that was not an admission by McCullough that he had racially abused Armitage.

Reid said: "Ulster and Matt McCullough strenuously deny the allegation, made by London Irish, of racial abuse towards Delon Armitage.

"Matt has apologised by way of letter for the use of foul language towards Armitage in the heat of the moment during the match.

"But this should in no way be misinterpreted as an admission to the use of racist language.

"We regard the allegation made by London Irish most seriously, as Ulster has an unblemished record in relation to racial issues."