Experienced reserve goalkeeper Paul Crichton will now make his debut for the Fills against Yeovil on Saturday.
Boss Neale Cooper said: "It's disappointing to lose Jason because he's been brilliant for us.
"It just about sums up the nightmare we are having on the injury front.
"But we have an experienced replacement in Paul. He'll come in at the weekend and I'm sure he'll do a good job for us."