Ulster Rugby has promised to "robustly investigate any complaints received" after Simon Zebo let it be known on social media that he was the target for abuse at the Kingspan Stadium on Saturday.
The Ireland international was replaced at half-time, reportedly as a 'tactical' decision, before tweeting how "I hope my ears deceived me with some comments directed my way from the crowd."
It was a terrible way to conclude the Irish provinces' clean sweep on the field, not least Ulster's 26-22 defeat of Racing 92.
The excuses were lined up. Iain Henderson was out. John Cooney pulled out with a back problem.
They had their problems. They also had Jacob Stockdale, the Ireland wing shooting clear for two tries that gave the All Whites the cushion they need to put Racing 92 to sleep.
Munster still have their work cut out for them as Exeter Chiefs gutted Castres 34-12 at Sandy Park to reduce the gap at the top of Pool Two to four points.
It sets up a tasty decider in Limerick next Saturday (KO 5.30, BT Sport) when only the winners are likely to move on to the quarter-finals.
Connacht will need to win away at Bordeaux-Begles next Saturday (KO 3.0, Irish time) to seal a Challenge Cup quarter-final after David Horwitz's late penalty secured a 20-18 win over Sale.