He has undergone further scans on the injury, but Allardyce has suggested that the Irishman needs to overcome a mental block regarding his fitness.
"The specialists say there should be no problem with it, but I think he's got uptight about it," said Allardyce in The People.
"That's disrupted his technique and put a lot of pressure on those areas.
"He's just got to forget about it, the specialist has told him to just keep doing his prevention work, his goalkeeping work, but not to overdo it.
"I think he's overdone it by the will of wanting to get better and better."