England full-back Mike Brown has not yet been ruled out of Sunday's match against Ireland, with coach Graham Rowntree encouraged by his progress.
Brown, who was stretchered off in the 47-17 victory over Italy on February 14, was thought to be highly unlikely to feature at the Aviva Stadium this week.
But according to forwards coach Rowntree, the news is now positive regarding the Harlequins back as he came through Tuesday's fitness session strongly.
"It's great news that he's done that session today, he's still in the mix," Rowntree told Sky Sports News HQ.
"We will follow it day by day but the signs are that he's improving and he should complete the protocol in time and be available.
"As with every other concussion that's happened, we tick all of those relevant boxes. We've been diligent."
Meanwhile, second-row duo Geoff Parling and Courtney Lawes, along with prop Alex Corbisiero and flanker Tom Wood, are also progressing well.
"They're all in the mix and we see how they train as we always do on a Tuesday afternoon session," Rowntree said.
"Particularly for Courtney Lawes, he's not played since December 20. I was there watching, so we have to wait and see whether they need a game for their clubs or whether we're prepared to put them straight into a pretty hostile Test arena. We have to do what is right for the team."