Mike Brown is expected to miss the remainder of Harlequins' Aviva Premiership campaign with concussion-like symptoms picked up during the Six Nations.
The full-back recovered from a collision with Italy's Andrea Masi midway through the tournament to play in England's final games of the championship against Scotland and France.
However, Brown has not played for Quins since returning from international duty, and director of rugby Conor O'Shea has revealed that the 29-year-old is still suffering with symptoms from that collision.
"Mike has played just six league games for us this season and it looks like it will probably stay that way," O'Shea told reporters.
"He comes in to see the medics but until he's symptom-free, he won't resume any sort of training. It's probably the wrong turn of phrase but it's doing his head in because he can't train and is very frustrated. He has headaches throughout the day.
"If it's an ankle injury, you can grade it and set a timescale. This is more 'how long is a piece of string?' Are we worried? Of course we're worried. He didn't even enjoy his week away. I feel for him."
Quins are currently eighth in the Aviva Premiership standings.
