Essendon has suffered a big injury blow, with ruckman Tom Bellchambers set to be sidelined for up to two months with a knee injury, putting him in danger of missing Round 1 against Hawthorn.

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.

"Heโ€™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, heโ€™ll build up his football over a month after that and then heโ€™ll be pushing for selection."

However, Daniher should be able to return to full training in around a fortnight.

"Weโ€™ve got to find the balance between filling Joeโ€™s tank up for the season and also getting him to the point, from a football point of view, where heโ€™s ready to play at a high level," Crow said.

"Weโ€™ll be weighing that up as we go but Iโ€™d be thinking more the later end of the Community Series, than the front end."