Evatt has not featured since the 1-1 draw at Bristol City last month due to serious bone bruising on and around his knee and broke down on his return to training this week.
"It's not great," he told the Blackpool Gazette.
"I was feeling really good last week and started to step up my training, but I've had a reaction.
"I'm a while away from fitness now, I think. It's a case of waiting for it to settle down. It's a frustrating injury which could settle next week or take a month or two.
"I've never had bone bruising before and don't know a lot about it.
"What I do know is that it can take as long to repair as a fracture. It's not great news."
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