Fisher, who PNE sold to Middlesbrough in January for a reported £300,000 fee, suffered a freak knee injury at home during the summer.
Boro manager Neil Warnock said: "We’re not sure at the moment but it doesn’t look very good,”
"I’ll know tomorrow but it’s looking like an operation and you’re talking nine months so we’re not optimistic about that.
"From what he’s telling us it was a complete accident the way that he did it, with a mate slipping and falling on him and crashing onto his knee.
"It’s the back of his knee.”
Here is a round-up of all the news from the Championship, including the latest transfer talk and gossip.
9. Swansea skipper in demand
Swansea skipper Matt Grimes is attracting interest from Fulham, Southampton, Bournemouth and Southampton.(Daily Mail) Photo: David Horton
10. Ex-PNE defender Darnell Fisher could miss full season
Middlesbrough could be without former PNE right-back Darnell Fisher for the whole season because of a knee injury. (Hartlepool Mail) Photo: Alex Dodd
11. Luton pay for Leicester striker
Luton have signed Admiral Muskwe from Leicester for an undisclosed fee. He was on loan at Wycombe last season. (Luton official website) Photo: Andrew Kearns