Toulouse Rugby have issued a statement claiming that Trevor Brennan acted in response to "repeated provocation" by Ulster supporters during Sunday's game.
The club claimed fans had insulted Brennan's mother and that "such people have no place in any sporting arena".
They said his action was "inexcusable but humanly understandable" and will ask the ERC to launch an investigation into the behaviour of some supporters.
"Brennan is a generous player who always respects opponents," they added.