Thomas faced live pitching against reliever Keith Foulke in a simulated game Wednesday, the final step in his recovery from a strained right quadriceps muscle.
"I'm ready to go," Thomas said as he sat in Oakland's dugout before the A's game against Kansas City. "I've got enough to get around the bases, that's all I need. Two weeks from now I should be back to full speed."
Thomas has been on the disabled list since May 29, five weeks after he signed with Oakland following his release from Toronto. He will bypass a rehab assignment and be available to play for the A's when they start a three-game series in Boston on Friday.
"If we were in a different situation I might [go on a rehab assignment] but I can help this team right away," Thomas said of the A's, who began the day eight games behind the Red Sox in the wild card race. "Just with my presence alone I can help."
The slumping A's will welcome Thomas' bat into the lineup. Heading into Wednesday's game against the Royals, Oakland had dropped nine of 11 since the All-Star break and was 8-16 in July.
"Frank's very close," A's manager Bob Geren said. "He felt good. It was a highly competitive simulated game, if that makes sense. Keith was going hard at it and Frank was battling. It was fun to watch."
Foulke will be sent to Triple-A Sacramento to make the first of what is likely two to three minor-league appearances before rejoining the big-league club. Foulke is scheduled to pitch Saturday, though Geren was uncertain whether the right-hander would start or come out of the bullpen.
"Watching him pitch today, he looks close," Geren said. "I wanted Keith to get some different looks with a lefty and a smaller right-hander and also big Frank."