The 25-year-old joins a list of absentees that already included captain Paul Hanlon, Paul McGinn, recently-recruited centre-back Harry Clarke and key midfielders Joe Newell and Kyle Magennis.
Easer Road stalwart Lewis Stevenson, primarily a left-back, has been asked to fill voids at centre-back and in central midfield in recent matches, while also wearing the captain's armband.
"It's a shame to lose Demetri because he felt like he was getting back to his best condition and he was doing very well for us," said Maloney, who is waiting to learn the full extent of Mitchell's injury.
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"It's hard on the squad because we've got six really important senior players missing. It's maybe a bit of bad luck that they've all happened at the one time but we just have to deal with it.
"I don't want to labour the fact too much because we've got other good players in the squad but it definitely makes it harder for the squad, particularly when we've had lots of midweek games. We've had to use players in two or three different positions, players like Lewis Stevenson.
"Lewis has been excellent for me. He's showing attributes I knew he had but to do it in a number six position is very good. He certainly helps bring up the average age of the squad because otherwise we've got a very young outfield 10 at the moment. I can't speak highly enough of him."