Denorfia's move to the disabled list because of lower back tightness came a day after Opening Day starting right fielder Travis Buck was optioned to Triple-A Sacramento, even though he has fully recovered from shin splints and was ready to come off the DL.
The A's will go with four outfielders -- left fielder Jack Cust, center fielders Ryan Sweeney and Rajai Davis and right fielder Emil Brown. Infielder Donnie Murphy can also play in the outfield. Manager Bob Geren said Denorfia had been unavailable the last few days, which is why Murphy stayed in the game in left field after pinch-running on Wednesday against Baltimore.
Denorfia was batting .260 with no home runs and six RBIs in 25 games. He had not started since April 29 and had appeared in two of the A's last eight games.
Denorfia did have six hits in 17 at-bats with runners in scoring position.
Todd Wills is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.