Ronan Keating has revealed Boyzone were forced to leave an ill Keith Duffy behind in a Thai hospital as they had to fly to Australia for the next leg of their tour.
And he told how Keith, 44, had been "in a downward spiral" before being admitted to hospital.
Keith was unable to perform at the show in Bangkok on Thursday night, and Ronan revealed that he's not sure when he will be well enough to join his bandmates Down Under on their 25th anniversary tour.
Speaking on radio show Magic Breakfast, Ronan said Keith has undergone blood tests and is awaiting the results.
Ronan said: "We had to leave him in the hospital to get here because we have a show tomorrow night.
Keith Duffy rushed to hospital leaving Boyzone to continue tour without him
"He took ill before the show, he just went on a downward spiral."
"He came to the gig, he had a massive, really high temperature, the doctors arrived at the gig and they said it wasn't possible for him to go on in the state he was in.
He revealed that he still doesn't know what caused Keith's sudden illness at this point.
"We really don't know, we assumed it was food poisoning or something like that, but we don't know, there may be something else going on. We're waiting to hear back on the blood tests and whether or not he can travel.
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"So we're hoping he can be on a plane tonight in Thailand and be here for the show tomorrow, fingers crossed."
Boyzone's next show is scheduled for Perth on Saturday night, followed by a gig in Adelaide next Tuesday and Ronan says he hopes Keith will be "right" to join them there if he cannot make Perth.
Being one man down forced the band to improvise and Ronan described their Bangkok show as "hilarious".
Boyzone star Keith Duffy rushed to hospital after falling ill while on tour in Thailand
Ronan explained: "We had considered certain things, but not others. I had to take some of Keith's vocals and I didn't know the words.
"It was in When The Going Gets Tough, and I had no idea, no clue whatsoever.
"I just looked at Shane and handed the mic out to the audience and hoped that they'd sing along".
