The Ospreys say their second-row forward might be sidelined for up to eight weeks after undergoing keyhole knee surgery. Evans has struggled with an ongoing knee problem that surfaced during Wales' autumn Test defeat to Samoa almost three weeks ago.
"Ian has been troubled by an ongoing problem with his right knee since being unable to complete the Samoa game last month," Ospreys head physiotherapist Chris Towers said. "Investigations and consultations with specialists have resulted in him undergoing a keyhole procedure, as a result of which he will be sidelined for six to eight weeks."
Evans was among a number of Wales players who suffered injuries during a dismal autumn campaign that saw the reigning Six Nations champions lose against Argentina, Samoa, New Zealand and Australia.
His fellow locks Alun-Wyn Jones, Bradley Davies and Luke Charteris were all hurt at various stages of the series, as were the likes of wing George North, hooker Richard Hibbard and prop Aaron Jarvis.
Wales begin their Six Nations title defence against Ireland in Cardiff on February 2, which is followed by a Paris appointment with France seven days later.
Evans could regain full fitness before then, but he is set to miss the Ospreys' remaining four Heineken Cup pool games against Toulouse (home and away), Leicester and Treviso.
- Sports & Recreation