Harlequins prop Joe Marler has been cited for an alleged kick at Grenoble's Arnaud Heguy in Friday's European Challenge Cup semi-final.
England forward Marler was playing his first game since serving a two-match ban for calling Wales' Samson Lee a "gypsy boy" during the Six Nations.
Marler appeared to aim a kick towards the head of Heguy in Quins' 30-6 victory at The Stoop and could now find himself in further trouble.
A European Professional Club Rugby statement read: "EPCR has received a citing complaint against the Harlequins prop, Joe Marler, following the European Rugby Challenge Cup semi-final match against Grenoble on Friday, 22 April 2016.
"Marler is alleged to have kicked the Grenoble hooker, Arnaud Heguy, in the 26th minute of the match at The Twickenham Stoop in contravention of Law 10.4 (c)."
After the match, Marler was defended by his coach Conor O'Shea over the incident.
"It was not a boot, it was nowhere near a boot - it was a shin," O'Shea said. "Any test for a citing has to pass the red-card test. 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."
Bans for kicking an opponent range from four weeks for a low end sanction, while a top end punishment carries a 12 to 52 week ban.
If found guilty, Marler could miss the Challenge Cup final versus Montpellier on May 13.