In a blog on his official website, the singer lamented: "Alas, my back's frigging knackered."The day after Belfast was spent in bed with it completely spasming - like toothache 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 40-year-old Take That star has also had to miss out on his own charity football tournament Soccer Aid.Instead of playing as planned, he was relegated to helping manage the England side that took on the Rest of the World.