Mako Vunipola will miss the climax to Saracens' pursuit of the double after being ruled of the rest of the season by a significant hamstring injury.
Vunipola lasted just half an hour of the Champions Cup final victory over Leinster on Saturday before being forced off alongside fellow prop Titi Lamositele, who will also miss the Gallagher Premiership title push.
A date for Vunipola's return has yet to be confirmed, but Saracens director of rugby Mark McCall insists the British and Irish loosehead will be available for England's World Cup campaign.
'Mako has a torn hamstring. We're waiting to see exactly what happens with that, but I very much doubt he'll play again this season. Neither will Titi,' McCall said.
'Mako won't be out of the World Cup, but he'll be out for a while. It's quite a significant injury.
'It's disappointing to lose two players of that quality and it makes us a little bit vulnerable.'
Vunipola, who is considered the game's standout loosehead, missed a large chunk of the Six Nations with an ankle injury and then suffered another injury to the same joint that resulted in an aborted comeback.
The showdown with Leinster in Newcastle was only his second match since the Championship rout of France in mid-February.
Along with in-form tighthead Lamositele, he will miss the home play-off at Allianz Park on May 25 and the final a week later - if Saracens progress.
Both players were due to be rested as part of sweeping changes for the climax to the regular Premiership season at Worcester on Saturday.