London - Mako Vunipola will miss the climax to Saracens' pursuit of the double after being ruled out for the rest of the season with a "significant" hamstring injury, the club's director of rugby Mark McCall said on Thursday.
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 Premiership title push.
A date for Vunipola's return has yet to be confirmed, but Saracens' McCall said the British and Irish Lions star would 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. Nether 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, 28, missed a large chunk of the Six Nations with an ankle injury and then suffered another problem to the same joint that resulted in an aborted comeback.
The European final against Leinster in Newcastle was only his second match since England's rout of France in mid-February.
Along with in-form Lamositele, he will miss the home Premiership play-off at Allianz Park on May 25 and the final a week later, if defending champions Saracens manage to reach Twickenham.
Both players were due to be rested as part of sweeping changes for the climax to the regular Premiership season at Worcester on Saturday.