CLEVELAND — Yet another setback for Kimmie Meissner.

The 2006 world champion withdrew from this week's U.S. Figure Skating Championships on Monday because of a hip flexor injury she suffered running on a treadmill. The injury happened about a week ago, and Meissner said she aggravated it during training.

She returned to her hometown of Baltimore for physical therapy, but is still feeling pain.

"The decision wasn't easy and was not made lightly," Meissner said in a statement from U.S. Figure Skating. "... I tried to get on the ice, but I'm still experiencing pain doing jumps. I would not be able to compete at 100 percent as I had been planning."

Meissner burst onto the skating scene at the 2005 national championships, becoming only the second American woman to land a triple axel in competition. A year later, she surprised just about everyone by winning the world title with the performance of her career.

But she has struggled since then. She was a disappointing seventh at last year's nationals, earning a spot on the world team only because three of the top four skaters were too young to go.

She left longtime coach Pam Gregory last spring and moved to Florida to train with Richard Callaghan, who coached Tara Lipinski to an Olympic gold medal. But Meissner's results this season haven't been any better, with eighth-place finishes at both Skate America and Cup of Russia.

With a strong group of up-and-coming skaters, including reigning world junior champion Rachael Flatt, Meissner was considered a long shot to earn one of two spots on the world team, let alone regain her national title.

"I plan to get stronger and overcome my injury," Meissner said, "so that I can compete at the 2010 U.S. Championships."