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."
Stephen Crainey is back from suspension but may struggle to displace Bob Harris, who impressed in his absence at left-back during last weekend's 2-0 home win over Blackburn.
Midfielder Chris Basham remains a major doubt due to ankle ligament damage, however manager Michael Appleton remains hopeful he can play a part in the festive programme.
Winger Matt Phillips (toe) stays on the sidelines.