However the 28-year-old lock has impressed with the speed of his recovery and Ospreys head coach Steve Tandy admits he could be back in action sooner than expected.
The RaboDirect PRO12 fixtures against Newport Gwent Dragons on Monday and Zebre on January 4 could come too soon but Tandy believes Evans could feature against Leicester in the Heineken Cup on January 13.
"Ian is an outside possibility to be in contention for the Leicester match," he said.
"He is up and around and moving pretty well so it is something we will review after the Dragons and Zebre matches."
In the absence of Evans, flanker James King, 22, has impressed in the second row - earning a new three-year deal with the club in the process.
"We're absolutely delighted that James has signed on for an extended period of time with us," Ospreys forwards coach Jonathan Humphreys.
"He's a guy we picked out of nowhere a good few years back and all of a sudden you see a kid going out to Toulouse, running a lineout for the first time, doing it very, very well."