U2 frontman Bono burst back onto rock's center stage on Friday after a two-month absence for a back injury, as the Irish band resumed what its manager predicts will be the most lucrative concert tour in history. 

U2 shook a packed Olympic stadium in the northern Italian city of Turin as Bono strutted, pranced, jogged and danced with little sign of being a 50-year-old rock star just 10 weeks off spinal surgery.

"I don't really know how to hold back, is the problem. You have to let the songs sing you at a certain point," Bono told Reuters just before relaunching the second leg of U2's 360 Degree Tour, so called because fans surround a giant circular platform.

U2 and Bono, who said he had done rehabilitation work for three to four hours a day, kicked off a rousing set with "Beautiful Day" and "Magnificent." They also played two new tracks called "North Star Acoustic" and "Glastonbury."

Bono thanked the cheering crowd for letters and emails he had received wishing him a speedy recovery.

"This band is like a family. It's a family business, U2. I am the prodigal son. I would like to thank my brothers for their patience," the leather-clad Bono told the crowd, referring to his bandmates.

POSTPONEMENT, MAJOR LOSSES

The singer underwent emergency back surgery in May after injuring himself. His subsequent rehabilitation forced the band to delay the North American leg of the tour until 2011.

U2 began the tour in Barcelona in June 2009.

The band's manager Paul McGuinness said Bono had trained hard to get back to performing and the band had done some recording during his recovery.

"That's a process that goes on all the time," McGuinness told Reuters. "The doctors are very confident. They certified him fit to perform. It's really a very short time for a spinal injury."

U2's tour is widely expected to be a strong point in a weak concert season hit by low sales.

"This tour by the end of this year will be the biggest grossing music tour by anyone of all time," McGuinness predicted. "And we will still have another 30 shows next year, 20-30 shows next year."

He added that the group would probably gross somewhere between $650-700 million by the time the tour ended in 2011.

That would top the record $558 million generated by the Rolling Stones' 2005-2007 Bigger Bang tour, according to music industry publication Billboard Boxscore.

McGuinness said that rescheduling the North American tour had brought "enormous" complications.

"It was extraordinarily difficult to reschedule these events, because it's an outdoor show. But very few numbers of people have asked for refunds, and most of the shows were sold out."

He said the band had lost around $15 million as a result of the disruptions, half of which was covered by insurance.