James Haskell has been ruled out of Wasps' European Champions Cup crunch clash with Toulouse on Saturday, but England team-mates Joe Launchbury and Elliot Daly have been passed fit.
Haskell lasted just 35 seconds of his comeback against Leicester Tigers last weekend following a lengthy absence due to a toe injury after seemingly being knocked out when tackling Freddie Burns, leading to concerns over his availability for the Six Nations.
The flanker did not do any serious damage, but Wasps director of rugby Dai Young said he will not be risked for a huge Pool 2 encounter at the Ricoh Arena.
"James is fine within himself, but he took a significant bang to the head on Sunday and we don't feel it right to push him to meet the tight deadline for a six-day turnaround," said Young.
"We would obviously all like for James to be involved in our big game against Toulouse, James included, but the most important thing is for him to feel completely right and under no pressure to make the game this weekend.
"This is first time he has suffered concussion and we have told him to take extra time, with the aim of being fit for Zebre [a week on Sunday] in the final pool round."
Launchbury was a doubt for England's Six Nations opener against France on February 4 due to a calf injury, but Wasps on Wednesday revealed that the lock is in contention to face Toulouse.
Daly came off for a head injury assessment during the Premiership win over the Tigers, but the utility back is set to face the Top 14 side.
England head coach Eddie Jones has a number of injury problems to contend with ahead of the Six Nations, with Joe Marler the latest to be ruled out for the start of the tournament due to a fractured of his lower leg.