The 20-year-old singer is taking it easy after undergoing major throat surgery last month but - although the odds are in his favour - his bandmates have concerns over whether his singing voice will ever be the same.
The group's Jay McGuiness said: "Whether his vocal range is affected or his singing, he'll definitely always be part of the group."
Max George added: "He's only young so chances are he's going to be okay. Obviously there's that underlying worry because it was a huge operation he had, but the signs so far have been really good."
The boy band - which also includes Siva Kaneswaran and Tom Parker- have had to delay recording their new album until Nathan is ready to sing again after the operation, to repair a haemorrhaged nodule on his vocal chords.
The band also said they have sourced the most qualified medics they can find to give Nathan - the youngest member of the band - the best chance of a full recovery.
Jay said: "We're getting the best people we can. He's definitely in better spirits than when he first came round."