South African Rugby has confirmed that Springboks captain Siya Kolisi underwent knee surgery last week and said it is unclear if he will be fit for this year's Rugby World Cup.
Reports emerged late last month that the loose forward, who lifted the Webb Ellis Cup in Japan four years ago, suffered a partial tear to his anterior cruciate ligaments playing for the Sharks against Munster in the BKT United Rugby Championship.
Ireland face South Africa on 23 September in Pool B of the World Cup.
"Kolisi underwent the operation on Friday and Springbok team doctor Jerome Mampane and his medical team will continue to monitor his recovery and rehabilitation," governing body SA Rugby said in a statement.
"Mampane said it was too early to make any reliable forecasts on when Kolisi may be able to return to play."
SA Rugby and Kolisi's club had remained tight-lipped about his condition over the last 10 days. The player's wife Rachel first confirmed the surgery via social media at the weekend.
Kolisi, one of the most respected figures in the game, is due to move to French club Racing 92 after the World Cup, which runs from 8 September to 28 October.
It is now a race against time for the 31-year-old to make the squad for the tournament in France.
"We wish Siya well during his recovery and we know that he will do everything possible to return to play soon as possible," said Springboks coach Jacques Nienaber.
South Africa, who name their final 33-man squad on 8 August, begin their title defence against Scotland in Marseille on 10 September.
The Sharks face Leinster in the BKT URC quarter-finals this Saturday.
Meanwhile, Scotland forward Jonny Gray (above) is in serious danger of missing the Rugby World Cup after dislocating his kneecap.
Gray sustained the injury during Exeter's 47-28 Heineken Champions Cup semi-final defeat by La Rochelle on Sunday.
"It’s relatively serious without being the worst it could be," said Exeter rugby director Rob Baxter.
"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.
"It’s a patella tendon injury, he’s dislocated his kneecap.
"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."
Second-row Gray, 29, has won 77 caps for Scotland and his absence from the World Cup in France would be a huge blow for Gregor Townsend’s side.
Scotland start their World Cup campaign against defending champions South Africa in Marseille on 10 September and face Ireland on 7 October.
Pool B also includes Six Nations Grand Slam champions Ireland, Romania and Tonga.
Watch the BKT URC quarter-finals, Leinster v Sharks (Saturday, 5pm) and Glasgow Warriors v Munster (Saturday, 7.35pm), on RTÉ2 and RTÉ Player, follow a live blog on the RTÉ News app or RTÉ.ie/Sport or listen to live commentary on Saturday Sport on RTÉ Radio 1.
Follow a live blog of Ulster v Connacht (Friday, 7.35pm) or listen to live commentary on Game On on RTÉ 2fm.
Additional report: PA
