The Manchester concert would have been Cheryl Cole's first for months in the UK.
Gary Barlow has said 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 U.S. 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 on Monday joked that he was now thinking of contingency plans for the event which he has put together.
"She is ill. We are waiting to hear. It's meant to be a surprise but that's the plan - if not, I don't know what we are going to do. I might just have to get on the piano and do a bit of Roll Out The Barrel," he said while speaking at rehearsals in London.
The X Factor judge said he was relishing the prospect of performing again, rather than observing and mentoring.
"I am always trying to remind myself that's actually what I do and I don't just sit behind a desk talking. So it's important to me to get back out there. I am looking forward to it I really am, " he added.
Barlow admitted it was hard work organising the charity event, and said he had made sure everything was in hand before the X Factor live shows began in August.
He also brought together Chipmunk, Ed Sheeran, Miss Dynamite, Rizzle Kicks, Tulisa Contostavlos and Labrinth for this year's BBC Children In Need single, Teardrop.
He asserted, "The message is to look after each other. And with the line-up of MCs we have got these are what young people listen to and so it's really important to have people that actually matter to young people speaking through their music."
Barlow, who mentored X Factor contestant Frankie Cocozza until he bowed out of the show amid drug allegations, said it was also important for those on the X Factor to remember they were in the public eye.
"It's important I think always to remember that there's an audience out there who are going to respond to anything that happens during the show and I think this year, as with most other years it's had its ups and down and it's important for us to remember we're actually setting examples," Barlow explained.
"And also for us to paint a picture of, although we're on a show here, this is what it's going to be like, this is how tough its going to be, which is why we always come from a position of honesty when we're giving our critiques," he concluded.