Scotland lock Jonny Gray has dislocated his kneecap and "is a major doubt" for the World Cup in France, his club, Exeter Chiefs, have confirmed.
The 29-year-old, capped 77 times by his country, sustained the injury during Exeter's Champions Cup semi-final defeat by La Rochelle on Sunday.
The Scots' first World Cup match is against South Africa on 10 September.
"It's relatively serious without being the worst it could be," Exeter director of rugby Rob Baxter said.
"From what I've been told, unless the operation goes exceptionally well and his recovery is exceptionally quick, I would say he is very doubtful for the World Cup.
"Fortunately, the other major ligaments within the knee are all stable. It's a relatively complex patella tendon injury, which is going to require surgery this week, and there's a relatively long period of rehab.
"We are hopeful to have him back fairly early next season, especially with the Premiership starting late next year with the World Cup first."
Source: BBC Rugby Union News