Sprinter Usain Bolt will miss both meets in Zurich and Brussels while he receives treatment to loosen his back. (Boris Horvat/AFT/Getty Images)

World sprint champion Usain Bolt will miss the rest of the track season because of tightness in his lower back, his agent said on Tuesday.

Manager Ricky Simms wrote in an email that a doctor examined Bolt in Germany, and the sore back "restricts his ability to generate power in his stride." Simms also said racing "in this condition could risk injury" to Bolt's legs.

Bolt had an MRI exam, which also revealed his previous Achilles tendon injury had healed.

The 23-year-old Jamaican will miss both meets in Zurich and Brussels while he receives treatment to loosen his back.

"I am very disappointed to miss two of the top meetings on the circuit — Zurich and Brussels — but trust that it is better for me not to take any risks this year," said Bolt.

"2011 and 2012 are very important championship years, and I hope to be back fully fit and healthy," said Bolt, referring to next year's world championship in Daegu, South Korea, and the London Olympics.

The news comes only four days after Bolt was upset by American Tyson Gay at the Stockholm Diamond League track and field meet.

Bolt laboured through both the preliminary heat and final. Simms said the decision to end Bolt's season was made "with a view to his future career."

The world-record holder in the 100 and 200 metres then ran a pedestrian 9.97 to finish second. It was his first 100-metre loss in more than two years.

"We wish Bolt, who has had a long history of back trouble, a speedy recovery and look forward to seeing his incredible talent delight us all once again next season," IAAF spokesman Nick Davies wrote in an email Tuesday.

Bolt smashed his own world mark in the 100 en route to a breathtaking 9.58 seconds at last year's Berlin world championship.

In that same event, he bettered his own world record in the 200, crossing the finish line in 19.19 seconds.

"I wish Usain the best as he gets healthy for 2011 and 2012. I would have liked for us to race again this year, but it didn't work out," Gay said. "I've had my own injuries in the past, so I understand his decision as well as anyone."

When healthy, Bolt has blown away the competition and is biggest draw in the sport of track and field.

"He is the most known athlete we currently have, and he's definitely someone that the public asks for," said Patrick Magyar, the director of Zurich's Weltklasse meet and vice chairman of the Diamond League. "If he was just not in the best of shape, he would still have come, but he is obviously at risk of hurting his body — and nobody wants that to happen."

With files from The Associated Press