Lillis, 21, played in Tuesday night's 3-0 win over Cheltenham Town after United's first choice goalkeeper Joe Murphy suffered a groin injury in the afternoon.
He was full of confidence after a loan spell at Notts County earlier in the season and says the manager Nigel Adkins can count on him if ndded on Saturday
"I just jumped straight in and felt confident, but I think the loan spell at Notts County earlier in the season helped that. I'll be ready for it if I'm needed," he told the Scunthorpe Telegraph.
United need to avoid defeat in Saturday's game at Glanford Park to secure a place in the end-of-season play-offs. If they lose then Tranmere will take their place.