Wasps will not risk James Haskell’s fitness this weekend when they take on Toulouse in the European Champions Cup unless the England flanker fully recovers from the blow to the head that left him unconscious last Sunday, just 36 seconds into his first match in more than six months.

Haskell was a second-half replacement in Wasps’ 22-16 victory over Leicester Tigers at the weekend in what was his first appearance of the season after having surgery on a toe injury, but he was knocked unconscious when attempting to tackle Tigers’ fly-half Freddie Burns.

Haskell was taken off the field and must now go through the mandatory six-day graduated return, World Rugby’s protocol over any head injuries, and after the 31-year-old’s girlfriend, Chloe Madeley, posted a picture on social media that revealed the large bruising to the flanker’s head, director of rugby Dai Young confirmed on Tuesday that Haskell is losing the race to recover fully in time for Saturday’s European crunch clash.

"He's probably doubtful, he's still with the medics today,” said Young. “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.

"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 per cent right.”

Wasps head into the match with Pool 2 finely balanced, as the Coventry-based side are equal on points at the top of the group with Toulouse as well as reigning Pro12 champions Connacht – who beat Wasps 20-18 last time out in round four.

The Aviva Premiership side will want to have one of their most destructive players available for the clash, given that a victory at the Ricoh Arena could set them up perfectly to top the group as their final pool game is against whipping boys Zebre, while Haskell also has his own motives to get back on the field.

Haskell saw Northampton Saints captain Tom Wood flourish in the No 7 shirt he vacated during the autumn internationals for England, but with Chris Robshaw ruled out of the upcoming Six Nations as he requires shoulder surgery, an extra place has been made available in Eddie Jones’s starting back-row.

But Haskell is running out of time to prove his fitness, having not played any rugby bar the 36 seconds against Leicester since England’s summer tour of Australia last year, and with other options such as Harlequins’ Jack Clifford and Leicester’s Mike Williams fit again, Haskell is running short on time ahead of next month’s tournament.

Despite his need for minutes on the pitch though, Young will not take any risks if he doesn’t improve by Wednesday.

Haskell had not played since England's tour of Australia last June (Getty)

"We may take a decision a little bit later in the week that it may be unwise for us to keep on waiting,” Young added.

"The next 48 hours will have a big bearing and if he's looking 100 per cent and passed everything we may continue with the process. If he's not right then it'll be a non-starter anyway."