England flanker Chris Robshaw could miss the Six Nations as he waits to discover the severity of a shoulder injury.
The 30-year-old has been in fine form since losing the England captaincy in December 2015, but was injured during Harlequins' 24-17 Premiership defeat at Worcester Warriors on New Year's Day.
Robshaw was due to have an initial scan this week and has now been ruled out of Quins' match against Sale Sharks on Saturday.
He will see a specialist early next week to decide the best form of recovery, with England's Six Nations opener against France less than a month away.
A Quins statement detailed Robshaw's options as: "either an extended period of rest and rehabilitation, or an operation."
England centre Manu Tuilagi has already been ruled out of the tournament with a knee injury suffered playing for Leicester Tigers.