The 35-year-old signed a one-year deal when he returned to the club in September, but has yet to make a first-team appearance at the club.
“I’m just about to sign a new contract so it is very pleasing because I really enjoy being at this football club,” said Marshall.
“It can be frustrating (being back-up goalkeeper) but I’ve gone from number three to number two.
“It will be hard to dislodge Brad Friedel who has been phenomenal and it will take an injury, not loss of form.
“It’s not being defeatist, it’s being realistic.”
