Saracens captain Kyran Bracken suffered concussion during Sunday's Zurich Premiership clash against leaders Gloucester at Vicarage Road and will be sidelined for three weeks.
He will serve the mandatory rest period in accordance with IRB regulation 10.1 that states:
"A player who has suffered concussion shall not participate in nay match or training session for a minimum period of three weeks from the time of injury, and may only do so when symptom free and declared fit."
The 41-times-capped scrum-half was expected to skipper England A when they faced France in the Six Nations A Championship.
But Bracken should be fully fit when Saracens take on Bath Rugby (Heineken Cup winners in 1998) in mid-April.
Better news for Saracens is that Thomas Castaignede, who scored a try and a dropped-goal in the first ever Heineken Cup final in 1996, has recoverd from injury and expected to play for France in their Six Nations opener against England on February 15.