The 13th-seeded Haas and four-time defending champion Federer were scheduled to play in the fourth round Monday.

"To pull out of this match, against Roger on Centre Court _ which is why you play the game _ is obviously very disappointing," Haas said. "Can't even put it in words."

Now the top-ranked Federer will face 2003 French Open champion Juan Carlos Ferrero or unseeded Janko Tipsarevic for a berth in the semifinals.

Because Haas pulled out before the match, it goes into the books as a walkover, and Federer will not get credit for a victory. So the Swiss star's winning streak at Wimbledon stays at 31 matches, and his record run on grass courts stays at 51.

Haas said he expects to be sidelined for up to a month with the lower abdominal injury, which flared up during his 1-6, 6-4, 7-6 (5), 6-4 victory over No. 21 Dmitry Tursunov in the third round Friday.

Haas called for the trainer during the second set, when he was treated and given painkillers. The German said the pain felt much worse Saturday and that tests showed the muscle was bleeding.

The match against Federer was to be the 29-year-old Haas' first in the fourth round at the All England Club.

"Who knows if this opportunity comes again," Haas said. "I certainly hope so."

He lost in the third round on four previous occasions, including in 1998 after beating Andre Agassi on Centre Court in the second round _ a victory that Haas noted on Sunday means he is undefeated at Wimbledon's main arena.

Once ranked as high as No. 2, Haas has struggled with injuries, including missing all of 2003 after two operations on his right shoulder.