Earnshaw has missed the last two games with a hamstring injury and is facing a race against time to return to action this weekend.
"I think Robert has a 50-50 chance of playing at the moment," said Calderwood.
"We've got to be 100% sure that we're not going to really damage him and have him unavailable for six to eight weeks if he were to rip that hamstring."
Defender Wes Morgan is in contention to feature after completing a one-match ban, while Calderwood has also hinted on-loan Brighton defender Joel Lynch could be handed his home debut.
Lewis McGugan (thigh), Paul Anderson (thigh) and Joe Garner (knee) continue to miss out for rock-bottom Forest.
Neil Danns is close to returning for Crystal Palace.
The former Birmingham midfielder has been sidelined since March with a groin problem, but he scored for the reserves in midweek to prove his fitness.
Danns will not be rushed back but he could make the bench at the City Ground.
Strikers Alan Lee, James Scowcroft (both hamstring) and Calvin Andrew (knee) are still missing so on-loan West Brom frontman Craig Beattie keeps his place after netting the only goal in Tuesday's derby win over Charlton.
Boss Neil Warnock is likely to name the same starting line-up for the third successive game, with left-back Clint Hill expected to play despite an ongoing groin problem.
Sporting Life