Clarke has returned to training after a knock but boss Alex Neil does not know whether he will be fit enough to feature against the in-form Cottagers.
Neil expects Paul Gallagher to be available after the midfielder was taken off in Tuesday’s win over Bristol City after complaining of a tight hamstring.
Sean Maguire, who has been named in Ireland’s squad for the forthcoming international friendlies, will be hoping for a start.
Fulham will monitor Tomas Kalas ahead of the trip to Deepdale.
Kalas has missed the last two games with a hip injury but has returned to training and boss Slavisa Jokanovic will assess him after Friday’s session.
That is Jokanovic’s only concern and he is unlikely to tinker with the side that breezed past Sheffield United on Tuesday.
That 3-0 success was their 14th Championship game without defeat, of which they have won 11.
Brighton have been linked with a swoop on League One Sunderland for the signature of goalkeeper Jason Steele.
Southampton remain in the hunt for Red Bull Salzburg's Amadou Haidara and are reportedly readying a £15million offer.
Aston Villa are reportedly weighing up a summer move for out-of-favour Huddersfield defender Michael Hefele.
Southampton are lining up a summer bid for Huddersfield Town midfielder Aaron Mooy, reports claim.