Surprise 2009 U.S. Open quarterfinalist Melanie Oudin (oo-DAN) says she has a muscle-damaging condition that may be caused by intense exertion.
Oudin has written on her Twitter feed that her "off season is a little paused at the moment" because of the ailment, called rhabdomyolysis (rab-doe-my-OL-uh-sis), and she is "doing everything possible for a speedy" recovery.
Her agent, Sam Duvall, confirms to The Associated Press on Monday that Oudin sent the tweets.
Oudin, who turned 22 in September, is ranked 129th. At 17, she pulled off a series of upsets, including against Maria Sharapova, to reach the U.S. Open's final eight.
Heavy exertion can cause muscle cells to leak enzymes and protein into the blood. Symptoms of rhabdomyolysis can include muscle pain and severe cases can lead to kidney damage.