On-loan Tottenham midfielder Pritchard, a key player for the Bees this season, missed the midweek trip to Sheffield Wednesday with a slight calf problem.
Striker Long, on loan from Everton, was also absent at Hillsborough after taking a knock to his knee and midfielder Diagouraga suffered a wrist injury during the 1-0 defeat.
Scott Hogan remains a long-term absentee as he recovers from cruciate ligament damage.
Mark Davies could be handed his first start in five months for Bolton.
The midfielder returned from a long-term knee problem as a substitute against Charlton last time out and Wanderers boss Neil Lennon is hopeful he can throw him in from the off.
Emile Heskey and Eidur Gudjohnsen both reverted to the bench having started against Norwich at the weekend and will come back into contention as Lennon continues to manage the pair whose combined age is 73.
The Trotters remain without Max Clayton (ankle), David Wheater (hamstring), Simeon Slavchev (ankle), Darren Pratley (hamstring), Marc Tierney (broken leg), Craig Davies (hamstring) and Zach Clough (shoulder).