The 28-year-old British and Irish Lions forward was taken off on a stretcher with anterior cruciate ligament damage during Wales' 27-13 defeat last week, an injury that was quickly ruled serious enough to keep him out of the Six Nations Championship that starts in February.
Yet the even worse news for the 60-times capped forward emerged with a statement on the Ospreys website reporting: "Dan Lydiate has been ruled out for the rest of the season.
"Following consultation it has been confirmed that surgery is required, as a result of which he will not play again until next season."
It is the latest major injury setback for Lydiate who missed the summer tour of New Zealand after suffering a shoulder injury when Wales were beaten by England in May.
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(Reporting by Ian Chadband; Editing by Tony Jimenez)
