London - England prop Joe Marler could face further disciplinary action after appearing to kick Grenoble hooker Arnaud Heguy in the head during Harlequins' 30-6 win over the French side late on Friday.
The 25-year-old was playing for the first time since serving a two-match ban for his "Gypsy boy" slur against Welshman Samson Lee in the Six Nations.
But Marler found himself in trouble again thanks to the 26th-minute clash with Heguy in the European challenge cup semi-final.
European competition officials have 48 hours from the end of the match to bring a citing against Marler, and any ban could leave him a doubt for England's June tour to Australia.
"Any test for a citing has to pass the red card test, and this does not pass that test," said Harlequins boss Conor O'Shea.
"Should he do it? No. Is it a red card? No. It's disappointing to have to talk about it because I thought his scrummaging was excellent.
"But he is under the microscope.
"Things happen, we never condone it but if that is a red card there's a heck of a lot of things that happen on the pitch that are worse."
Citing commissioner Iain Goodall will now determine whether Marler should face a disciplinary hearing for the incident.
Marler initially escaped censure for his taunts against prop Lee in England's 25-21 Six Nations victory over Wales at Twickenham on March 12.
Global governing body World Rugby later intervened and called a misconduct hearing however, dissatisfied with the leniency of Six Nations and RFU bosses.
Marler admitted the charge and was banned for two matches and fined 20,000.