|RBS Six Nations: Ireland v England|
|Venue: Aviva Stadium, Dublin Date: Sunday, 1 March Kick-off: 15:00 GMT Coverage: Live on BBC TV, HD, Red Button, Radio 5 live, Radio Ulster FM, the BBC Sport website, mobile, the BBC Sport app and Connected TV.|
England head coach Stuart Lancaster says full-back Mike Brown is not yet symptom-free after suffering a concussion against Italy.
Brown, 29, was stretchered off in the first half of England's 47-17 win over Italy at Twickenham on Saturday.
He will not train this week but could be fit to face Ireland on 1 March.
"We will go through the return-to-play protocol and will see how it plays out over the next three or four days," Lancaster told BBC Sport.
"It's too early to say about his availability for Ireland.
Ex-Ireland wing Denis Hickie on concussion:
"Players could come off in the past having not remembered the last part of the game. That no longer happens.
"The protocol, analysis and treatment of blows to the head is different, it is far less arbitrary. I don't doubt that the medical procedures and protocol - while evolving - are much better."
"It's being treated in the same way any other concussion would be treated," Lancaster added.
"He's got to be symptom-free before he starts even the graduated return-to-play and he's not been symptom-free for the last 24 hours, so obviously we're not even going to start the process until that's clear.
"We haven't got a game this weekend, which does help. If we did have a game, the fact that he's not symptom-free now means he probably would automatically be ruled out."
Brown is the only injury concern from the England squad that beat Italy at Twickenham, with Saracens' Alex Goode likely to start in Ireland if the Harlequins player is not available.
Players return to clubs
The England starting XV that faced the Italians have all been retained in camp this week, along with the Exeter wing Jack Nowell and Gloucester centre Billy Twelvetrees, who replaced Brown on Saturday.
The remaining squad players have been released to play for their clubs in the Premiership this weekend.
Among those available for their clubs are Sale fly-half Danny Cipriani and Harlequins number eight Nick Easter, who both scored tries after coming on as replacements against Italy, and Northampton lock Courtney Lawes.
Lawes, flanker Tom Wood and lock Geoff Parling are all expected to be fit to train next week but will struggle to force their way into the match-day squad according to Lancaster.
"If you have a team that is playing well and you have some consistency of selection and two wins, it does become harder to change the team, particularly in the light of guys coming back from injury who haven't played for a while," added the England coach.