Jetta was injured in a VFL practice match between Casey Scorpions and Box Hill on Saturday March 10.
Melbourne football manager Josh Mahoney confirmed the luckless Jetta - who played just nine games in 2011 after suffering a broken hand in round 12 and having a post-season shoulder reconstruction - has been placed on the club's long-term injury list.
He is the third player on Melbourne's long-term injury list, joining ruckmen Max Gawn (knee) who is out for the season, and Jake Spencer, who is returning from a knee reconstruction he had at the start of 2011.
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This means Melbourne has the opportunity to elevate three more rookies if it chooses to, in addition to James Magner, who was elevated as the club's nominated rookie ahead of the League's Tuesday deadline.
However, Mahoney said the Demons are in no rush to elevate any more rookies at this stage.
"Our timing for that is when we think it is appropriate, [when the rookies] are in serious AFL consideration," Mahoney said.
Meanwhile, Colin Sylvia continues to recuperate at home from a back injury he suffered on Friday night against Port Adelaide. He is making good progress and Melbourne is hopeful he will be well enough to return to the club in the next few days.
Mahoney said the talented midfielder is still expected to miss four to six weeks.
