Mike Brown is still suffering concussion symptoms and faces a race against time to prove his fitness for England's pivotal RBS 6 Nations clash against Ireland in Dublin.
England boss Stuart Lancaster has revealed the Harlequins full-back is yet to start the first steps in the strict recovery process after a heavy blow to the head in Saturday's 47-17 victory over Italy.
England have sent 17 players back to their clubs to play Premiership rugby this weekend, but Courtney Lawes, Geoff Parling and Tom Wood are unlikely to be fit for league action.
Full-back Brown will not train this week, but must remain free of any concussion symptoms for 24 hours before he can resume normal service.
"We're going to have to see how he comes through the return to play protocols. He'll go through that graduated return and he hasn't started that yet," said England head coach Lancaster.
"He won't take any part in training this week. So if he starts all that tomorrow then he goes through that process, so that would be from the bike and onwards.
"Seven days would give him enough time in the build-up, but that's hypothetical at the moment because he hasn't started the process, so we'll wait and see."
England pack trio Lawes, Parling and Wood have been released back to their clubs, but Lancaster does not expect any to be available for league action this weekend.
The England boss hopes all three will train fully next week ahead of the Ireland clash, which is already being billed as the Six Nations decider.
Lancaster admitted, though, that Lawes faces a "tough ask" to break back into the match squad to face Ireland as he continues to recover from ankle surgery.
"Geoff Parling, Tom Wood and Courtney Lawes still haven't trained fully yet, so it's unlikely they'll be available this weekend for the clubs," said Lancaster.
"But they should all be available to train fully next week: then obviously a decision needs to be made from our point of view whether to include them in our squad for Ireland.
"It's what we expected with Courtney, he wasn't under the illusion he would be playing this weekend.
"He knows it's going to be a tough ask to get in the team not having played for so long, but we'll wait and see how this weekend plays out.
"They are all slightly different in terms of how much rugby they have played this season and when their original injuries were sustained.
"Geoff obviously came back from a long injury but then picked up the knee injury in the European Cup; Woody picked up a knock on the same weekend but has played a lot more rugby.
"So they are all slightly different really, but we've equally got a fully-fit pack from the weekend and the bench as well, Nick Easter and Tom Croft.
"Obviously someone could pick up an injury with their club this weekend, so we'll just have to wait and see how it plays out next week."
Lancaster admitted Saracens' Alex Goode is in pole position to replace Brown if the first-choice full-back does not make it in time to face Ireland.
"Alex Goode was excellent at the weekend: it's the best game I've seen him play in a while," said Lancaster.
"So he's right at the forefront of everyone's mind.
"Another option would be Anthony Watson to play at 15, and Jack Nowell obviously being in the squad. But the way Alex Goode played he'd probably be the next guy, but I don't want to pre-judge that."