Bellchambers had been on a modified training program due to a knee complaint, but will now require surgery.
Fellow big man, Joe Daniher, also has a knee issue and will be on a reduced training load.
“Tom, like Joe, has a knee surface issue from a number of years ago that raised its head before Christmas,” Essendon high performance manager Justin Crow said.
“He (Bellchambers) was in rehab after a rest and progressing well until a week ago.
“He’s not quite at 100 per cent so today we sought the advice of his specialist, Julian Feller, and Tom is going to go in for a clean-out of his knee to try to get him to 100 per cent.
“Tom will start running in a month, he’ll build up his football over a month after that and then he’ll be pushing for selection.”
However, Daniher should be able to return to full training in around a fortnight.
“We’ve got to find the balance between filling Joe’s tank up for the season and also getting him to the point, from a football point of view, where he’s ready to play at a high level,” Crow said.
“We’ll be weighing that up as we go but I’d be thinking more the later end of the Community Series, than the front end.”