DOUBT lingers over the fitness of Essendon captain Dyson Heppell as the gun midfielder attempts to be declared fit for Friday night's clash with Adelaide. 

The Bombers will fly to South Australia to take on the Crows in what looms as a pivotal game, with both sides sitting 9-7.

Heppell has unfused growth plates in both feet. He had surgery on the right one a few years ago to fix the issue, but his left foot is now giving him grief and has sidelined him over the past fortnight.

Tuesday's training session will be key to determining whether the 27-year-old returns.

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"There's a number of things that he has to tick off. I won't go into all of them. We'll know today whether he's ready to go," coach John Worsfold said.

Heppell joined in with the main group and looked to be moving freely. 

The Bombers seem to have hit form, having won three straight, but have been dealt another cruel injury blow after star defender Michael Hurley went in for left shoulder surgery on Monday.

Worsfold couldn't provide an update as to when the 29-year-old will be back.

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"Now it's just recovery time. Not sure of what timeframe. It's obviously going to be a number of weeks. We'll just play it by ear," Worsfold said.

He mooted a few replacements, including a potential debutant.

"Patty Ambrose we expect to be right to go but Brandon Zerk-Thatcher's been in wonderful form in the VFL, as has Michael Hartley. We've got some good options to consider," Worsfold said.

Ambrose has dealt with a quad strain suffered in the warm-up before Essendon defeated Greater Western Sydney in round 15.

Zerk-Thatcher is untried at senior level but the South Australian is aggressive and courageous.

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He has picked up at least 13 disposals in six of his past seven VFL games, with the exception being when he suffered a hand laceration and didn't play out the contest.

The 20-year-old stands 195cm and was drafted with pick No.66 in 2017.

Adelaide possesses an imposing forward line when it is firing, although Tom Lynch's expected absence with a tendon-related calf issue makes things easier for the Essendon defence.

However, Taylor Walker and Josh Jenkins loom large, while Hugh Greenwood is a threatening aerial target.