Clarke requires a double shoulder operation which could rule the former Bristol Rovers shotstopper out for the rest of the season but Wilder is not rushing to sign a replacement.
"Wayne will get us through this period and if not, we'll have to make a decision off the back of it," Wilder told the Oxford Mail.
"Wayne will pick it up. He didn't have a lot to do (at Bradford) and he just needed that game."
Striker James Constable is available again having served a fourth-match ban and he will be pushing for a recall along with usual strike partner Tom Craddock at the Kassam.
Deane Smalley and Adam Chapman come into contention after spells on the sidelines, while Lewis Montrose will hope to start again having made his debut in the win at Bradford.