Wasps scrum-half Joe Simpson will be out for 12 weeks after undergoing ankle surgery.
Simpson was expected to be sidelined for four to six weeks after sustaining an injury during the 51-10 hammering of Leinster in the European Rugby Champions Cup last weekend.
But the 27-year-old, who missed out on a place in Eddie Jones' first England squad, faces a lengthier lay-off than originally hoped following an operation.
Wasps have signed Craig Hampson on loan from Championship leaders Bristol due to the absence of Simpson, who is not expected to return before the Champions Cup quarter-final against Exeter Chiefs in April.
Dai Young, Wasps' director of Rugby, said: "It is obviously disappointing for everyone that Joe has had to undergo surgery on his ankle, especially at a time when he was playing so well and I'm sure he was knocking on the door for international recognition.
"His ankle was quite swollen, so it took a little bit longer for the results to come back, but he has had his surgery and we now wish him all the best for his recovery.
"Joe's injury leaves us a little light at scrum-half, so it is great that we have been able to bring in Craig so quickly. Craig has impressed in the Championship for both Bristol and Yorkshire Carnegie and we're looking forward to him joining up with the squad."