Humphrey has been called up to Jamaica's national side ahead of their World Cup qualifier against Panama, while Hume is with the Canada squad at their training camp in Spain.
Forward Jack King (foot) remains out after having surgery but Grayson has no other injury or suspension concerns.
Oldham will be without three players for the trip to Preston due to international duty .
Danny Philliskirk marked his Oldham debut by scoring twice as Lee Johnson's side eased through to the second round of the Johnstone's Paint Trophy with a convincing 4-1 victory at Shrewsbury and he will hope to retain his place.
And while Connor Brown is still sidelined with a knee injury, Johnson will check on Charlie MacDonald who has missed their last three games with a dead leg.
- Sports & Recreation
- Chris Humphrey
- Iain Hume
- Jeffrey Monakana