Casper Ankergren is set to make his first start of the campaign against Carlisle with Higgs struggling with a thigh problem.
Grayson told the club's website: "He (Ankergen) came on for Shane on Saturday and I've got no qualms about him whatsoever. But we're still trying to sign a loan goalkeeper to sit on the bench. A lot of calls have gone in and we'll see where we get to."
United have an option to recall Scotland u-21 international Alan Martin who is on loan at Accrington but that would prevent him from continuing his loan with the League Two club.