Croft has injured the medial ligament in his left knee
England flanker Tom Croft will miss at least the first two games of the Six Nations after injuring his left knee for the second time this season.
The blind-side suffered medial knee ligament damage in Leicester's Heineken Cup win over Viadana on Saturday.
He will miss England's games against Wales and Italy.
The Rugby Football Union say he has started his rehabilitation programme with a view to returning to action in five to six weeks.
If Croft returns on schedule, Leicester's Guinness Premiership match against Gloucester on 20 February would be his only chance of action before England's third game of the championship, against Ireland on 27 February.
England's final two matches are against Scotland on 13 March and France on 20 March.
"It's a blow to injure the same knee," admitted Tigers boss Richard Cockerill.
"England manager Martin Johnson might be concerned about Tom's Six Nations situation, my only concern is that we won't have him in Swansea next weekend.
"I have my job to do, Martin has his. But Crofty is a world-class player who hadn't seen action for ages. He needed playing time, so I had no qualms starting him."