NEW YORK - Maria Sharapova pulled out of the U.S. Open on Wednesday because of a right shoulder injury.
Earlier in the day, former top-10 player Mardy Fish pulled out of the men's side, the latest setback in his bid to make a comeback on tour after dealing with heart issues.
Sharapova, the 2006 U.S. Open champion, has played only one match on tour since her second-round loss at Wimbledon in June.
"Maria Sharapova is one of the great warriors of the tennis world," said Gordon Smith, executive director and COO of the U.S. Tennis Association. "If she withdrew, there's a serious issue."
Sharapova originally was seeded third at the U.S. Open. The USTA said 2012 Wimbledon runner-up Agnieszka Radwanksa would shift from No. 4 to No. 3, and all other seeded players below her would move up a spot, too.
The USTA said Anastasia Pavlyuchenkova would become the No. 32 seed. The draw for the year's last Grand Slam tournament is today. Play begins Monday.
Sharapova's surprising exit caps a tumultuous couple of weeks for the four-time major title winner and former No. 1 player.
The Russian was sidelined by a hip injury after Wimbledon. Then she hired Jimmy Connors as her coach, an arrangement that lasted all of one match, a loss.
Sharapova last skipped the U.S. Open in 2008, when she was off the tour for about 10 months because of surgery on her right shoulder.
On the men's side, the USTA said Fish, 31, cited "personal reasons" for his withdrawal. Fish's Twitter feed carried this message Wednesday: "Friends, unfortunately my health won't allow me to compete this year at the US Open. Thank you for all your support."
The American has missed months of action at a time over the past two seasons. On Tuesday, Fish stopped playing in the third set of his match against Jarkko Nieminen at a hard-court tournament in Winston-Salem, N.C., because of heat stroke.
Fish has played only eight matches on the ATP World Tour in 2013, going 3-5. He skipped all of the Grand Slam tournaments this season while entering only five other events on the main tour.
A year ago, Fish reached the fourth round at the U.S. Open but withdrew before he was to face Roger Federer at that stage, saying it was for "precautionary measures" on doctor's orders. Fish missed about 2 1/2 months earlier last season because of an accelerated heartbeat.
The night after he lost a match at Key Biscayne, Fla., in March 2012, Fish's heart started racing uncontrollably. That May, doctors induced extreme palpitations to try to pinpoint the problem. He returned for last year's Wimbledon.