EDMOND, Okla. — Fred Couples withdrew from the U.S. Senior Open on Thursday because of a back injury, and Craig Stadler and Graham Marsh also pulled out of the event next week at Oak Tree National.

Couples, second in the 2010 tournament, was replaced by John Harris, the first alternate from the Byron, Minnesota, sectional qualifier.

Stadler also cited a back injury, and Marsh, the Australian who won the 1997 U.S. Senior, pulled out because of an undisclosed injury. Stadler was replaced by David Ishii, and Marsh’s spot went to Bruce Vaughan.