Usain Bolt is calling it quits for 2010, cutting his season short because of tightness in his lower back less than a week after losing in the 100 meters to American rival Tyson Gay.

Bolt's manager, Ricky Simms, said in an e-mail yesterday that the world record-holder at 100 and 200 meters will have treatment to loosen his back and then rest, skipping IAAF Diamond League track meets in Zurich on August 19, and Brussels on August 27.

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

"2011 and 2012 are very important championship years and I hope to be back fully fit and healthy.

"I would like to thank everyone for their support and look forward to coming back stronger next year."

Simms said Bolt was examined on Monday by a doctor in Munich who found the back problem.

"He has a tightness that restricts his ability to generate power in his stride and continuing to race in this condition could risk injury to his hamstrings or calf muscles," Simms wrote.

Bolt's manager said the decision to take a break was made "with a view to his future career."

Simms also said that an MRI exam showed that a previous left Achilles' tendon injury is healed.

Bolt hadn't lost an individual race in two years until Friday, when Gay beat him at the DN Galan meet in Stockholm.

Gay ran 9.84 seconds, and Bolt finished in 9.97.

Afterward, even Gay acknowledged he wasn't racing against a fit Bolt.

"I'm really happy with the win," Gay said at the time, "even though Usain Bolt isn't in the best shape."

When Bolt is at his best, no one comes close to him. And no one else in his sport is as big a draw.

"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."

The Jamaican stole the show on the track at the 2008 Beijing Olympics, winning gold medals and breaking the world records in the 100 and 200 sprints, as well as the 4x100 relay.

None of the finals in those events was even close, and Bolt began his celebration in the dash before it was done, stretching out his arms with palms up, then slapping his chest.

He followed that up at last year's world championships in Berlin by lowering his marks in the 100 to 9.58 seconds and in the 200 to 19.19.