JAMES Gwilt's future is unclear after the Essendon defender underwent surgery on a knee injury on Tuesday.

The 29-year-old, who is out of contract at the end of this season, suffered the injury in the Bombers' loss to Richmond last Saturday.

He has already gone under the knife but the club does not know if the former Saint will be able to return to the senior line-up by the end of the season.

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Essendon high performance manager Justin Crow said the results of the surgery would determine if Gwilt will play again this season.

"James has got an injury to the cartilage in his knee – the meniscus," Crow told the club's website.

"He's been in for surgery this morning with Julian Feller. We'll be waiting for the outcome of that surgery before knowing what's going to happen for the rest of the year.

"It's just arthroscopic surgery but given there is only six games to go, we're a bit unsure where that leaves us."

Bombers top-up player Nathan Grima could come back into the club's VFL side after an extended layoff with a hip injury.

If he gets through training on Thursday Grima looks set to be selected, but fellow top-up Mathew Stokes will miss at least another week with a groin injury that has sidelined him for two weeks.

Back-up ruckman Mark Jamar is progressing ahead of schedule after suffering a hamstring injury against West Coast in round 15.