Saracens may be without Mike Rhodes for their European Champions Cup semi-final with Racing 92 at the weekend after the starting flanker was cited Monday for headbutting during his side's quarter-final win against Leinster.
"Rhodes is alleged to have committed an act of foul play in that he struck the Leinster centre, Robbie Henshaw... with his head in the second minute of the match," said a European Professional Club Rugby statement.
A suspension for Rhodes following that 25-17 win in Dublin would be a further setback for Saracens, who are already without suspended fly-half Owen Farrell.
An independent disciplinary committee will hear the case by video conference on Tuesday.
Under World Rugby's foul play laws, striking with the head carries a sanction of a six-week ban for a low-end offence, 10 weeks for mid-range and from 16 to 104 weeks for a top-end offence.
In Saturday's other semi-final Exeter host four-time champions Toulouse.