(Reuters) - U2 lead singer Bono has undergone emergency surgery on his back in a Munich hospital after being injured while preparing for the next leg of the band’s world tour, a spokesperson said Friday.

The 50-year-old from Ireland had been preparing for the North American leg of the “360 Degree” world tour which is due to kick off in Salt Lake City on June 3.

“Bono has today undergone emergency back surgery for an injury sustained during tour preparation training,” his spokesperson said.

“He was admitted to a specialist neuro surgery unit in a Munich hospital.

“Bono will spend the next few days there, before returning home to recuperate. Once his condition has been assessed further, a statement will be made regarding the impact on forthcoming tour dates.”

After North America, the tour was scheduled to travel to Turin in Italy on August 6. It was not immediately clear how badly the injury would disrupt the group’s tour.

The tour earned around $109 million (75.5 million pounds) in 2009, according to music journal Billboard, making it the world’s most lucrative, and the publication also predicted it would end up being the highest-grossing tour in history.

By some measures the band, with hits like “Sunday Bloody Sunday” and “Where the Streets Have No Name,” is the world’s most successful. They have sold more than 150 million records, according to unofficial estimates.