Saracens forward Theo McFarland is set to miss the rest of the season after suffering an anterior cruciate ligament injury in training.
"Everyone knows, not how difficult it is to come back from an ACL, but how painstaking the process is," said Saracens director of rugby Mark McCall.
Saracens hope to have England forwards Maro Itoje and Jamie George available for Saturday's home game with Exeter.
George missed the loss to the Exiles because of a heel injury, while Itoje has not played since 11 December due to concussion protocols.
However, Samoa international McFarland will not feature in any of the north London club's remaining Premiership or European Champions Cup fixtures as he recovers from the knee injury.
"It's a shame because Theo made a lot of progress very quickly," said McCall.
"But we have a great medical team and he'll come back well and he'll come back strongly. When he does, he'll get better and better.
"Now we just feel sad for him."