ESSENDON'S defensive stocks have suffered another blow with Matt Dea ruled out for the start of the season with a knee injury.

Dea, who played 12 games for the Bombers in 2018, has suffered a medial collateral ligament (MCL) strain and is expected to miss six weeks.  

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Forced to watch on during Monday's session at Tullamarine, Dea will be confined to a knee brace for the next fortnight.  

Dea was delisted at the end of last season before earning a reprieve via the rookie list.  

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His setback comes as first-choice defender Martin Gleeson continues to work back to full fitness after an ankle injury sustained in last year's pre-season.

Gleeson has joined Josh Begley (ACL) and Mason Redman (ankle) in parts of training with a view to being ready in the first half of the season.

"Those three players, we’ve seen them in full football drills, (but) none of them are ready to be involved in match play as of yet," Bombers physical performance manager Justin Crow said.

"They’re all tracking at the moment, all going well, towards playing some football around AFL round one.

"We just want to have a really careful progression with each of those players given how the amount of time they’ve missed."

The Bombers face Carlton in the opening match of the JLT Community Series at Ikon Park on Thursday night.