Manager Paul Dowsell confirmed the news after his forward picked up the serious knee injury at Leyton Orient on Saturday.
“When he had the initial scan we hoped it was just a tear,” the manager told the club’s website.
“But the MRI scan showed that he had ruptured his cruciate ligament, and also torn his meniscus and his anterior ligament. It’s very similar to what Ross Worner did last summer.
“The knee will be allowed to settle down first and Tommy will hopefully have his operation in about 3-4 weeks, after which the recovery period will be about six months, so he’ll be back with us for pre-season training.
“I’m devastated for Tommy and for the club, because he was getting better and better this season.
“But it needn’t be the end of the world. Alan Shearer had a similar injury and came back from it, and with the treatment these days players can recover completely from injuries like this.”
He added: “We’ll support him through it, as we always support injured players and look forward to seeing him back in action next season.”