Centre Manu Tuilagi is out of England's opening Six Nations match against Scotland on Saturday because of an ankle injury.
Head coach Stuart Lancaster said he was confident Tuilagi would be in full training next Tuesday or Wednesday and available for the game against Ireland.
Prop Alex Corbisiero will miss the whole Six Nations after undergoing an operation on his knee.
As expected, fly-half Freddie Burns has returned to his club Gloucester for treatment on his knee and will miss at least the first two matches.
Lancaster will name his team for the Calcutta Cup match on Thursday.
Tuilagi, 21, was devastating during last autumn's record 38-21 victory over world champions New Zealand, scoring one try and creating two more.
"By the end of the week we expect Manu to be running fully and changing direction," Lancaster said.
"He will be training fully by Tuesday or Wednesday next week, but I'll need to make a call earlier in the week. He won't be training properly until at least Friday.
"Manu is a big loss - he was outstanding against New Zealand. But he missed the first two games of last year's Six Nations because of a hamstring and it's an opportunity for someone else."
Tuilagi's absence means Lancaster will have to find a new partner for Brad Barritt of Saracens, with Gloucester's Billy Twelvetrees and Jonathan Joseph of London Irish the other centres in the squad.
Owen Farrell and Toby Flood, the only two fly-halves in the squad, are possible alternatives.
"We have a pretty good idea of how we'll rejig the midfield. We have our thoughts," said Lancaster.
"Brad will be in the equation and we need to make sure we can still break the gain line and have physical defenders. We've got to have the ability to get across the gain line and defend."
In Corbisiero's absence, Harlequins loose-head Joe Marler is likely to regain the starting role he relinquished to the London Irish player in the autumn, with Saracens' Mako Vunipola the other alternative in the elite squad.
The initial outlook on Corbisiero's knee problem was that he could return against France on 23 February but London Irish director of rugby Brian Smith revealed on Sunday that his rehabilitation will take longer.
Lancaster, however, denied Smith's suggestion that the injury is more grave than has been made public.
"The reality is the surgeons recommended two weeks rest and said it would then take six to eight weeks to be back playing, so that will rule him out of the Six Nations," said Lancaster.
"Hopefully he'll be back around the final game against Wales, but the reality is he'll have to play two or three Premiership games first.
"Alex is a big loss, but Joe Marler has played well for Harlequins recently. Mako Vunipola is improving all the time and Nick Wood was outstanding for the Saxons."
Burns, who made an impressive debut as a replacement against the All Blacks, will also have to put his Six Nations ambitions on hold for the time being, leaving the fly-half spot a straight choice between Owen Farrell and Toby Flood.