The field wont be set until Monday afternoon. Should anyone withdraw after that, his opponent would get a bye into the second round at La Costa Resort.
Bjorn has struggled the past several years with neck and back problems. He is the second player to withdraw, with Sergio Garcia saying two weeks ago he needed time off to rest.
Craig Parry of Australia was the first alternate, but told tour officials he wouldnt be coming to the Accenture Match Play Championship, so Ames became the first alternate. Next in line was Trevor Immelman of South Africa.
If the brackets arent changed, first-round matches Wednesday will include Woods-Ames, Vijay Singh against Graeme McDowell, Phil Mickelson against Charles Howell III and Ernie Els against Bernhard Langer.