Defending champion Andre Agassi [Images] has pulled out of this week's Cincinnati Masters to protect his troublesome back.

The 35-year-old American made the decision after he was beaten by Rafael Nadal [Images] in the final of the Montreal Masters on Sunday, his second tournament in three weeks.

"I can't start anything any more that I can't be sure I'll finish," Agassi said.

"Ten weeks ago I made a commitment to myself that I would only play when I can [give it everything].

"I'm not 100 percent, that's something I just have to cope with, and it's obviously really disappointing but I have to take care of my body."

Agassi missed Wimbledon [Images] because of the injury and, though he has been taking cortisone injections, he wants to avoid further injury with the US Open [Images] just two weeks away.

The American, three times a winner in Cincinnati, flew to the city on Monday to explain his decision to tournament organisers.

Agassi said he has not ruled out further cortisone injections in the two weeks before the US Open, but said he is excited about the year's final Grand Slam event.

"Ten weeks ago, I didn't know where things were going to go," he said. "I'm just so glad to be healthy, and to be chasing down balls I know I can't get, let alone ones I know I can."

At 35, Agassi is the elder statesmen of the tour, but he repeated his vow to continue playing as long as he can compete at the top level.

He even hinted that if he won the US Open, he would not follow in the footsteps of Pete Sampras [Images], who quit after his emotional victory, over Agassi, in 2002.

"I don't know how long it's going to be [that I keep playing] but I have no interest in tying a nice little ribbon around my career. I'm not ready to let anyone take over yet."

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