England forward Dylan Hartley has been cited for alleged foul play during Northampton's Heineken Cup defeat against Ulster on Friday.
The Saints captain has been reported by match commissioner Jean-Claude Legendre for striking his opposite number, the Ulster hooker Rory Best, with his arm, European Rugby Cup announced.
No date has yet been set for Hartley's disciplinary hearing.
Hartley has only just returned to action after suffering an injury that kept him out of England's autumn Test campaign.
Earlier this year, the New Zealand-born hooker was banned for eight weeks after being cited for biting the Ireland flanker Stephen Ferris during an Six Nations match at Twickenham.