The ex-Algeria international was forced off in the second half of United’s 1-0 loss to Perth Glory on Saturday with the injury.

Matmour has been cleared of a fracture but is no guarantee to be fit to play in Saturday’s home clash with in-form Newcastle Jets.

The Reds, who are winless in their past three matches, are already without a series of key players.

Taylor Regan (ankle) and Tarek Elrich (knee) are long-term absentees, while Vince Lia (knee), Johan Absalonsen (thigh) and Ersan Gulum (lung) are still several weeks away and Baba Diawara is close to returning from a hamstring problem.

Reds goalkeeper Paul Izzo, who impressed with a penalty save in the 1-0 loss to Perth, said United were feeling the effects of the injuries.

“It’s obvious we’re not blessed with the deepest squad,” Izzo said.

“I think hopefully if we can get a few boys back it’ll make a massive difference.

“We’ll see what that is this week.”