Mathieu Bastareaud could be handed a lengthy ban for an apparent homophobic slur aimed at Benetton Treviso's Sebastian Negri during Toulon's European Champions Cup win on Sunday.
The France centre appeared to call Negri a "f***ing f****t" in the closing stages of the Top 14 side's 36-0 victory at Stade Mayol after taking exception to something the lock said to him.
Bastareaud - who faces a potential suspension ranging from six weeks to a year if found guilty of verbally abusing Negri, ruling him out of at least the beginning of the Six Nations - claimed he was provoked by Negri.
However, he has since expressed his remorse for comments he made to his opponent.
He tweeted: "Good evening everybody, I want to apologise for my response to the insults of the Italian Player.
"I reacted badly in responding to his provocation, I am sincerely sorry for the people I hurt."
A citing complaint was made against Bastareaud and European Professional Club Rugby will review the incident.