ESSENDON'S Cale Hooker and Michael Hartley are both battling hamstring problems.
Hooker was forced to sit out Saturday's match simulation at Tullamarine and will remain on a "very individual" training program until at least mid-March.
The 28-year-old tall appears no certainty to feature in the JLT Community Series.
"Cale is going to be on a very individual program all the way up to round one, which is going to be a big priority in getting him to play there," Essendon high performance manager Justin Crow told the club's website.
"We’re going to be very selective in what he does and doesn’t do between now and then.
“We’re really happy with ‘Hooksy’ and he’s had a big pre-season to date.”
Hooker has returned to the club after his season-long suspension, and has been training as a forward.
Scans have confirmed Hartley has an inflamed hamstring, but it is hoped he could return to training within a fortnight.
The 23-year-old defender left the track early on Saturday.
"Fans who came to the game would have seen Michael limp off fairly early in the piece. We had him scanned – in his hamstring he’s got some minor fascial irritation that has shown up," Crow said.
“It’s really not of much concern to us and he’ll be back into training within the next fortnight.”
Hartley played 19 games last season to prove a bonus for the Essendon defence in a trying year which ended with the wooden spoon.
The club says Tom Bellchambers is progressing well following knee surgery last week.
Joe Daniher is set to resume full training soon, having also been battling a knee complaint.
The Dons faces Collingwood in the opening game of the JLT Community Series on Thursday February 16.