Gary Barlow says a planned duet with Cheryl Cole for Children In Need hangs in the balance because she is unwell.
The Take That star had been lining up an appearance with Cole at the Children In Need Rocks event in Manchester on Thursday.
It would be Cole's first performance for months in the UK, in a year which saw her unceremoniously dumped as a judge from the US version of X Factor.
But Barlow said it was still not clear whether it would go ahead because the Girls Aloud singer was feeling "ill".
It is understood that organisers have been informed she is having problems with her throat.
Barlow joked that he was now thinking of contingency plans for the event which he has put together.
Speaking at rehearsals in London, he said: "She's ill. We're waiting to hear.
"It's meant to be a surprise but that's the plan - if not, I don't know what we're going to do. I might just have to get on the piano and do a bit of Roll Out The Barrel."
The X Factor judge said he was relishing the prospect of performing again, rather than observing and mentoring.
"I'm looking forward to it I really am," he said.