Wales flanker Dan Lydiate will not play again this season after suffering a knee injury.
Lydiate suffered anterior cruciate ligament damage during Wales' victory over South Africa in Cardiff last Saturday.
Lydiate needs surgery and will miss the Six Nations and he will almost certainly be unavailable for the British & Irish Lions tour of New Zealand next summer.
A statement on the Ospreys website read: "Following consultation it has been confirmed that surgery is required, as a result of which he will not play again until next season."
Lydiate has been a mainstay in the Wales back-row under head coach Warren Gatland, forging a powerful breakaway unit alongside Sam Warburton and Taulupe Faletau.
Wales have cover, with skipper Warburton an option at blindside flanker, along with Gloucester's Ross Moriarty.
It is the second major injury blow that Lydiate has suffered this year.
He captained Wales against England at Twickenham in May, but was laid low by a shoulder problem during that game which ruled him out of Wales' subsequent three-Test tour to New Zealand.