The All About You hitmakers are due to hit the stage at the De Montfort Hall in Leicester, England but the singer admits getting through the gig is going to be a struggle.
Taking to Twitter.com shortly before showtime, he writes, "Got a slight sore throat today, gonna need some help singing tonight Leicester!"
The illness isn't the only problem Fletcher and his bandmates Dougie Poynter, Danny Jones and Harry Judd faced on Monday.
Fletcher reveals, "Our tour bus broke down today. Fun times. Made it to the venue in time for dinner. Bosh."