The 40-year-old star is playing a series of UK shows but said his back was "knackered" as he goes through his paces for the performances on his Swings Both Ways tour.
The on-off Take That star told how he had to sit out the annual Soccer Aid charity football match he organises because of the difficulties he was having.
And in a new blog on his website he told fans: "Alas, my back's frigging knackered. The day after Belfast was spent in bed with it completely spasming - like tooth ache under my shoulder blades.
"Oh the joys of getting older. These things are sent to test us. By whom and why, I'm not sure. But one thing's for sure - the show must go on, and it will."
The singer is renowned for his energetic performance but told earlier this month how the wear and tear on his body meant that he even had to scale back on his beloved football.
The Port Vale fan was on the bench for Soccer Aid and explained at the time: "I've got two discs rubbing together on my back.
"I can't get the insurance to play because I'm in the middle of a tour - if I do the back in out on the pitch, the tour goes kaput."
His next show is at the Metro Radio Arena in Newcastle on Sunday and he is due to play the SSE Hydro in Glasgow on Thursday, June 26.