Ben Morgan is likely to miss England's entire Six Nations campaign after fracturing his leg on Friday.
The Gloucester No.8 was one of England's most impressive performers in the autumn internationals but his 2015 has been derailed after being stretchered off in his side's 24-23 win over Saracens.
Morgan, 25, underwent surgery on his left leg on Saturday but Gloucester remain hopeful his rehabilitation programme can begin in the coming weeks.
A statement from the club read: "Morgan has suffered a fracture to his lower left leg and had surgery performed on Saturday morning. He will commence an appropriate rehabilitation programme for this type of injury over the coming weeks."
Saracens' Billy Vunipola and Wasps skipper James Haskell are in contention to replace Morgan.
England have already lost Wasps lock Joe Launchbury, who faces three months on the sidelines after undergoing neck surgery in December.
Coach Stuart Lancaster will announce his Six Nations squad after the upcoming round of European club games, which take place on 17 and 18 January.
England begin their Six Nations campaign in Cardiff against Wales on 6 February.