Manu Tuilagi is struggling to be fit for the start of England's Six Nations campaign after being ruled out for four weeks with a hamstring problem.
The centre, 20, suffered the injury playing for Leicester on 27 December.
England face Scotland on 4 February and Tuilagi could also be a doubt for the trip to Italy the following week.
Leicester club-mate Louis Deacon is definitely out of the tournament - the second row faces four months on the sidelines with a torn hamstring.
Tuilagi, who has seven caps, started each of England's five matches at last year's World Cup.
Having only recently returned from a broken cheekbone, Tuilagi limped out of the victory at Sixways and subsequently missed Leicester's 28-23 win over Sale before scans revealed he faces another month on the sidelines.
The Leicester pair's absence is another blow for interim coach Stuart Lancaster, who has dropped Danny Care after the scrum-half's arrest for drink-driving.
Second row Courtney Lawes is also facing a race against time to be fit for the start of the Six Nations after injuring his knee.
After breaking into the international side in the build-up to last year's World Cup Tuilagi was expected to play a key role under Lancaster.
The Tigers centre was viewed as one of few successes for England in New Zealand, although he attracted criticism for some of his off-field behaviour.
He was fined £3,000 for jumping from a ferry and swimming ashore in Auckland following England's quarter-final exit.
Tuilagi was also given a £4,800 fine by the International Rugby Board for wearing an unapproved mouthguard carrying the name of a sponsor.
Deacon, 31, tore a hamstring in the same game as Tuilagi was injured, the win against Worcester on 27 December.
The lock, who has 29 international caps, faces a long spell on the injured list and Tigers coach Richard Cockerill admits the player's absence is a significant blow to the Welford Road club.
Cockerill told BBC Radio Leicester: "He has a tear in his hamstring. We are waiting for the exact advice from the specialists on what to do but there will probably be three or four months of recovery time on that.
"It's disappointing for him with the Six Nations and getting back to some really good form for us. 'Deacs' has been massive for us leadership-wise so we'll miss him a lot."
Meanwhile, Leicester and England fly-half Toby Flood has sustained a knee injury. Cockerill said: "Toby had a bang on the knee and it's being treated. We'll just have to wait and see how it progresses."