England prop Mako Vunipola requires surgery on his hamstring and will be out for at least three months, the RFU have confirmed.
Vunipola played just half an hour of Saracens' Champions Cup final win against Leinster on Saturday, before succumbing to injury and leaving the field along with fellow prop Titi Lamositele, who will also be absent for the team's Premiership title run-in.
The injury will rule Vunipola out for the rest of the English domestic season, including the Premiership playoffs, and he now faces a race against time to be fit for England's Rugby World Cup campaign.
England face Wales in a pair of pre-World Cup Test matches on Aug. 11 and 17, while Eddie Jones' side also face Ireland at Twickenham on Aug. 24 and Italy in Newcastle on Sept. 6. England's World Cup campaign then kicks off in Japan against Tonga on Sept. 22.
Saracens' victory over Leinster in Newcastle marked just his second appearance since England's thrashing of France in February.