Jetta sustained the injury in Casey’s practice match win over Box Hill Hawks at Casey Fields on Saturday.
Football manager Josh Mahoney said it was still unknown how long Jetta would be sidelined.
“Unfortunately, Neville Jetta’s run of bad luck continued on the weekend,” he told melbournefc.com.au.
“After an extended layoff with a shoulder reconstruction, he hurt his ankle during the game.
“He has been assessed by the surgeon and has had scans, but at this stage, we’re still waiting for the results.”
But in better news for the Demons, Cale Morton is set to return from a knee injury.
Mahoney said impressive mature-age rookie James Magner would miss Melbourne’s final NAB Cup clash, due to a hand injury.
“James hurt it in the NAB Cup [round three] game,” he said.
“He suffered an open cut on his hand, which is a minor injury, and we expect him to be available for the season proper.”
Co-captain Jack Grimes faces a fitness test this round, but remains on target for round one.
“Jack’s rehab from his shoulder injury is progressing well,” Mahoney said.
“He has to get through a full training session and then be available for selection next week, which will be in preparation for round one.”
Long kicking Dee Luke Tapscott is also a chance to return, after battling a quadriceps niggle.
“Tappy pulled up sore in the quad while we were training last week,” Mahoney said.
“As we have with all of our other players, we’ve taken a conservative approach with Tappy.
“He’s had an extended layoff and we want to make sure he’s fit and raring to go, but he’s a test for this week’s game.”
Liam Jurrah will be sidelined for at least another month with a wrist injury.
Ruckmen Max Gawn and Jake Spencer are out with knee injuries. Gawn will miss the season, and Spencer is out for 6-8 weeks.
Rookie Michael Evans and first year Demon Rory Taggert are out indefinitely with back injuries.
Youngster Leigh Williams (back) is now two weeks away from returning.
Injury list
Michael Evans (back) - indefinite
Max Gawn (knee) - season
Jack Grimes (shoulder) - test
Neville Jetta (ankle) - TBA
Liam Jurrah (wrist) - 4 weeks
James Magner (hand) - 1 week
Jake Spencer (knee) - 6-8 weeks
Rory Taggert (back) - indefinite
Luke Tapscott (quad) - test
Leigh Williams (back) - 2 weeks
