England coach Stuart Lancaster admits he is concerned about the fitness of Manu Tuilagi ahead of the Six Nations opener against Scotland on 2 February.
Leicester centre Tuilagi, who scored one try and set up two others in England's 38-21 victory over New Zealand last month, is struggling with an ankle injury.
He was a late withdrawal from the Tigers side that beat Toulouse in the Heineken Cup on Sunday.
England have already lost flanker Tom Johnson for the whole Six Nations, while prop Alex Corbisiero and fly-half Freddie Burns will both miss the start of the tournament.
"I need a decision to be made early, by the weekend preferably, because if Manu is not available then there will be decisions to be made," Lancaster said.
"Richard (Cockerill, the Leicester director of rugby) said he was 70-30 in the lead-up to the game and they pushed him.
"Manu is pretty optimistic that he's going to be alright but I don't want to say now that he's going to be fit or vice-versa.
"We'll just have to wait and see how he gets on. It's too early to tell."
If Tuilagi cannot prove his fitness, Lancaster's most likely move would be to start with either Jonathan Joseph or Billy Twelvetrees alongside Brad Barritt.