The singer, who recently cut short a rescheduled Berlin show after feeling unwell, has subsequently cancelled this weekend's gigs in Holland's Rotterdam, Oberhausen in Germany and a date in Antwerp in Belgium.
The 'OMG' star's spokesman told WENN: "Usher is suffering from an upper respiratory illness which is currently preventing him from performing a proper show. After consultation with doctors, he has been advised to reschedule the upcoming dates in order to get the rest he needs to ensure a complete recovery."
Usher was quoted as saying: "I have been very excited about my European tour and I deeply regret having to reschedule the shows. I am truly sorry for any inconvenience I have caused my fans.
"My fans are the best in the world and I am looking forward to getting better so that I can give them the show they deserve."
Usher is due to kick off the UK jaunt of his world tour in Manchester on January 26.