England lock Joe Launchbury could miss the start of the Six Nations, Wasps boss Dai Young has revealed.
Launchbury, 23, has a nerve problem in his neck and missed the November Tests.
He was told he would need six to eight weeks of rest to recover but on Sunday Young admitted: "Joe's rehab isn't going quite as quickly as we'd like."
The lock will see his consultant next week and Young admitted he does not know if he will be back in "two or three weeks, or two or three months".
Launchbury was in the crowd to see Wasps bid farewell to Adams Park with a seven-try thrashing of Castres on Sunday.
Wasps boss Young added: "Fingers crossed it's not too serious and his rehab will pick up quickly.
"Sometimes the rehab goes quicker than expected, sometimes it goes slower. There are checkpoints and those aren't being reached as quickly as we'd hoped for.
"We have a good relationship with England, we work together on everything and the most important thing is to be getting Joe right.
"He has been out for a while and we want him back and 100%."
England start their Six Nations campaign away to Wales on 6 February, while the tournament runs until 21st March.