England captain Owen Farrell is set to miss the Six Nations opener against Scotland after suffering an injury while training with Saracens.
Farrell was retained as England skipper earlier this week by head coach Eddie Jones, despite not playing since November because of an ankle problem.
He had hoped to return against London Irish in the Challenge Cup on Sunday but has now been ruled out.
England play Scotland on Saturday, 5 February.
Farrell will see a specialist early next week and is now not expected to join up with England in their training camp in Brighton.
England will announce a squad update on Monday with Courtney Lawes favourite to take over the captaincy in Farrell’s absence.
“Owen Farrell suffered an injury in training this week ahead of the game against London Irish, ruling him out of the match,” said Saracens in a statement.
“Owen was back in full training having recovered from the ankle injury he sustained against Australia during the Autumn internationals.
“We will have a further update after he sees a specialist early next week.”
With Farrell’s involvement for the start of the tournament, at least, in doubt, Marcus Smith will be entrusted to run England’s attack from fly-half after impressing during the November Tests.
Joe Marchant, Henry Slade and Mark Atkinson are among the centre options available to Jones, while in-form Leicester 10 George Ford could now win a recall despite being surplus to requirements through the autumn.