Marshall, 29, has sat out in recent weeks with the knee injury as the Gladiators charge up the table has been halted.
Team mate Cleveland Taylor is also struggling with a knee problem.
Boss Dave Frecklington said: “Marcus and Cleveland are both having scans through the PFA.
“Marcus' swelling's been there for two or three weeks which is a concern and he could miss the rest of the season. We thought Cleveland would be out for a couple of weeks but it's going on two months now so it's a worry."
New loan signing Jonny Margetts missed training on Tuesday through illness and will be assessed on Thursday ahead of the Hyde trip when he hopes to make his Matlock debut.
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