That likely will involve right-hander Jesse Hahn, who posted a 3.35 ERA in 16 starts for the A's last season but was slated to start the season with Nashville after posting a 11.15 ERA in Spring Training.
Doubront was removed from Saturday's exhibition against the Giants after just one inning with forearm tightness.
Lambo, 27, hit .333 with two home runs and five RBIs in 25 games this spring.
Cash Kruth is a reporter for MLB.com. Follow him on Twitter at @cashkruth. This story was not subject to the approval of Major League Baseball or its clubs.