The 28-year-old has undergone keyhole surgery to cure the problem and will now rest up having hobbled off in the shock 26-19 defeat to Samoa last month.
Ospreys Head Physio Chris Towers told the Ospreys' website: "Ian has been troubled by an ongoing problem with his right knee since being unable to complete the Samoa game last month.
"Investigations and consultations with specialists have resulted in him undergoing a keyhole procedure, as a result of which he will be sidelines for six to eight weeks."
Born in Johannesburg, Evans impressed as a youngster with Pontypridd and Swansea before provincial giants Ospreys came calling in 2005 - going on to make his international debut in June of the following year.
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