Carroll, 25, is sidelined with an ankle injury which will see him miss the start of the Premier League season.
Having missed a large part of last season due to injury, the latest setback is a blow to Carroll and Allardyce's team.
Allardyce said Carroll was struggling to cope with having to spend more time off the field.
"He is pretty miserable," Allardyce said.
"He is not very happy with life at the moment because it is a massive blow to him again. We just have to pick his spirits up.
"Hopefully when the boot comes off and the specialist gives him the okay to start working again he will feel a lot happier with himself.
"But he is certainly very upset and very miserable at this moment in time."
Ecuadorian forward Enner Valencia has been brought in for a fee in the region of £12 million, but he too will miss the start of the campaign.
