Springboks' Kolbe out for up to a month with ankle issue
Kolbe, 29, sustained the injury in last weekend's French Top 14 win at Lyon.
The 2019 Rugby World Cup winner could miss up to four games.
"I'm speaking to the doctor and the physio but usually it's four weeks or a bit less," Kolbe told his club's RCTPlay platform.
"I would prefer if it was a bit less.
"I hope to be back on the field as soon as possible to play with the team again," he added.
Kolbe's season has been hampered with fitness issues after sustaining a broken jaw in July as well a thigh issue in November.
"It's been difficult, there's a lot of frustration, there's been a lot of injuries. But my focus is the team, working with the physio to get back on the field soon," he added.
The Springboks start the defence of the Webb Ellis trophy on September 10 against Scotland and they also play world number one side Ireland, Romania and Tonga in the group.