Mako Vunipola will miss the climax to Saracens’ pursuit of the Premiership title with a torn hamstring.
Vunipola was hurt during Saturday’s Heineken Champions Cup final win over Leinster and the 28-year-old will be out for “a minimum of three months”.
But Saracens director of rugby Mark McCall insists the British and Irish loose-head will be available for England’s World Cup campaign.
England’s first World Cup pool game in Japan is against Tonga on 22 September.
Before that, there are four warm-up fixtures scheduled for August and September and Vunipola is a doubt to participate in those.
Fellow Saracens prop Titi Lamositele will also miss the Premiership title push.
“Mako won’t be out of the World Cup, but he’ll be out for a while,” said McCall. “It’s quite a significant injury. It’s disappointing to lose two players of that quality. It makes us a little bit vulnerable.”
Vunipola 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.
His appearance at Newcastle’s St James’ Park was only his second match since the Six Nations win over France in mid-February.
He will now miss a home play-off semi-final on 25 May and, if Sarries progress, the final at Twickenham a week later.