ATLANTA -- Braves right-hander Charlie Morton doesn't know if he'll throw another pitch this season. Nor does the rookie hurler know what has caused the persistent back discomfort that he's felt for nearly two months.

The Braves have told Morton that they're going to shut him down for at least 10 days. During this time, they're hoping to get a better idea of what is causing the pain he has felt between his right shoulder blade and rib cage.

"I don't know how bad it is," Morton said. "It might be just something where I have to rest it a little bit."

Morton was hoping to have his back examined via an X-ray at some point this weekend. But for now, he and the Braves are left to wonder about the cause of the pain and the fact that he's lost nearly 20 pounds since the start of Spring Training.

"It doesn't keep me from throwing a ball," Morton said. "It just keeps me from throwing a ball without pain."

Morton said he believes he first started feeling the discomfort and realized a drop in his velocity after his third Major League start this season. Statistically, it's obvious to tell when the 25-year-old rookie right-hander began experiencing his inconsistencies.

During his first three big league starts, Morton was 1-1 with a 4.24 ERA. Opponents hit .258 against him and produced a .320 on-base percentage. Over the course of his next five starts, he posted a 9.53 ERA and allowed a .309 batting average with a .394 on-base percentage.

"It's just kind of off and on, in terms of how bad the pain is," Morton said. "I'd be interested to know to what degree it's affected me."

Morton, who is a power pitcher who relies on his four-seam fastball and curveball, was never able to make the adjustments that would have allowed him to pitch through the pain. He's received two cortisone shots, with the first one coming when the team was in Los Angeles in early July.

A few days later in San Diego, Morton limited the Padres to one earned run over 5 1/3 innings. The second cortisone shot came a few days before he limited the Marlins to two earned runs over six innings on Aug. 28.

After Morton returned to the mound on Tuesday and allowed the Marlins seven runs -- four earned -- in just 3 1/3 innings, the Braves decided it was time to give the rookie hurler an extended rest. They won't give him more than two cortisone shots in one season.

With the addition of James Parr, who provided six solid innings during his Major League debut on Thursday night, the Braves have five starters to fill their rotation for the remainder of the season.

Morton will continue to be evaluated over the next few weeks, and there's a chance he could return to the mound later this season. But combined with his time at Triple-A Richmond, he has already thrown 151 2/3 innings this year. Before this season, he'd never thrown more than 124 2/3 innings, reaching that total in 2005.