Chris Ashton could face a lengthy ban after being accused of biting an opponent during Saracens' 27-12 Premiership victory over Northampton Saints on Saturday.
The England winger was accused of the bite by Saints prop Alex Waller during the first half of Sarries' triumph at Allianz Park.
Waller and Ashton came together as they were tussling for possession on the ground, with the Saints man's arm around his opponent's neck.
As they grappled Waller claimed he was bitten by the 29-year-old, and asked referee Greg Garner to review the incident.
"Alex repeated at half-time in the dressing room what he said to the referee, that he had been bitten on the hand," said Saints director of rugby Jim Mallinder.
The citing commissioner will review the incident and Ashton could face a retrospective ban if found guilty.
Saracens boss Mark McCall defended his player, but admitted he had not seen the incident during Saturday's win.
"I've heard about but I haven't had chance to see it," he told BT Sport.
"I would be very surprised if that was the case, and hopefully it wasn't the case, but we will see it in the next few days I suppose."
Last season Ashton received a 10-week ban for putting his hand near the eyes of Luke Marshall during Sarries' European Champions Cup clash with Ulster, a suspension which ruled him out of the Six Nations.