London - England prop Mako Vunipola is in danger of missing the World Cup later this year after being ruled out of action for at least three months due to a hamstring injury.
The 28-year-old Saracens star, who missed most of the Six Nations campaign due to an ankle injury, will undergo an operation on the hamstring he injured in Saturday's Champions Cup final victory over Leinster.
"Vunipola's hamstring injury requires surgery and will take a minimum of three months to recover," Saracens said in a statement.
England fly to World Cup hosts Japan on September 8 and play their opening pool match against Tonga two weeks later.
Even if Vunipola's recovery takes the minimum three months, he will be forced to miss two of the four warm-up matches.