Jonny May's participation in England's upcoming Six Nations campaign hinges on a visit to a specialist this week, with the Gloucester wing set to miss at least the opening two rounds.
An ongoing knee problem has got progressively worse, resulting in his absence against Perpignan in the EPCR Challenge Cup on Saturday and subsequent withdrawal from Eddie Jones' 36-man training squad.
May has been an ever-present under Jones since 2017 and is an influential member of the backline, creating a highlights reel of spectacular tries, but he now faces a race against time to be involved in England's title quest.
"Jonny's seeing some people this week, but it will definitely be a good couple of weeks," Gloucester head coach George Skivington said. "He's seeing the best of the best.
"He's had a niggle for a little while and it kept him out of one game a few weeks ago. It's just been chipping away, and it got to a point where it wasn't great, so we decided to get it investigated.
"Once we know exactly what the story is, we'll have a better idea about the injury. It would have been one incident a few weeks ago, but he's been managing his way through it, as generally speaking senior players do, and it just got a little too much."
The February 26 showdown with Wales at Twickenham is the earliest he will be back, but the country's second most prolific try-scorer behind Rory Underwood could also be looking at a lengthier lay-off.
Elliot Daly, who can provide cover on the wing as well as at full-back and in the centre, was drafted into the England squad for this week's training camp in Brighton following May's withdrawal.
Freddie Steward, Jack Nowell and uncapped pair Ollie Hassell-Collins and Tommy Freeman are also options Jones currently has at his disposal to play out wide if May misses the entire tournament, although Skivington remains optimistic the 31-year-old will be able to play some part.
"The hope is that he will still play in the Six Nations," Skivington said. "If he can back involved in the Six Nations then great. It's unfortunate for Jonny because we'd like to see him playing for England.
"There aren't too many who will nail their rehab like Jonny. He's on it every day anyway when he's fully fit, doing all his pre-hab. When he comes back I'm sure he'll be absolutely flying."
Marler out of camp after positive Covid test
England's preparations for their opening match against Scotland at Murrayfield on Saturday, February 5 have suffered a further blow after Joe Marler was forced to withdraw from the Brighton camp after returning a positive Covid-19 test.
The prop returned the positive test on Tuesday morning and immediately went into isolation, with a second PCR test confirming the earlier result.
No other players or staff have tested positive and England are not expected to call up a replacement.
"Joe Marler has tested positive for Covid and has withdrawn from the England squad for this week's training camp in Brighton," a statement from the RFU said.
"After returning a positive lateral flow test on Tuesday morning, he immediately went into isolation. A subsequent PCR test taken that morning confirmed the result.
"All of the other England players and staff have undergone daily lateral flow testing - all of which returned negative results."