Wasps flanker James Haskell is losing his fitness fight to face Toulouse.
The 31-year-old England star is still being assessed by the club's medics and is running out of time to be ready for Saturday's European Champions Cup visit of the French side.
Haskell made his first appearance since playing for England against Australia in the summer -- after a toe injury -- in Wasps' 22-16 victory over Leicester on Sunday.
But he lasted just 35 seconds after coming on as a replacement when he seemed to be knocked out after tackling Freddie Burns, although walked off the pitch.
Haskell must go through the protocols introduced around concussion, a mandatory six-day graduated return, and director of rugby Dai Young admitted he is struggling to be fit.
"He's probably doubtful, he's still with the medics today. I think he'd really have to tick all the boxes so it's unlikely he's going to be fit -- although he's not ruled out," he said.
"We'll have a better picture towards the end of the day but if he isn't quite right then that's it because he hasn't got enough time. He has to tick every box and it would mean waiting until the morning of the game for him to be 100 percent right.
"We may take a decision a little bit later in the week that it may be unwise for us to keep on waiting.
"The next 48 hours will have a big bearing and if he's looking 100 percent and passed everything we may continue with the process. If he's not right then it'll be a non-starter anyway."
Wasps are joint top of Pool 2 with Toulouse and Connacht on 13 points with two games left and only the top side going through automatically.