He's been on the DL twice this year due to an injured right thigh, most recently going back on Saturday. He also sat out from May 28-July 31 because of tendinitis in his quadriceps.
The 40-year-old Thomas ended his season hitting .240 with eight home runs and 30 RBIs in 71 games. In 19 seasons in the majors, Thomas has a .301 average with 521 home runs and 1,704 RBIs in 2,322 games.
Only Ted Williams, Babe Ruth and Mel Ott finished their careers with a .300 batting average, 500 home runs, 1,000 runs and 1,500 walks. He is tied with Williams and Willie McCovey with 521 home runs, 17th on the career list.
The A's activated first baseman-designated hitter Mike Sweeney, who had surgery on both knees on June 11. Sweeney hit .292 with two home runs and 12 RBIs in 40 games before going on the disabled list May 29.
Sweeney hit .222 with one home run and six RBIs in nine games on an injury rehab assignment with Triple-A Sacramento.
Sweeney, 35, played his entire career with Kansas City before this season. He hit .292 with 197 home runs and 837 RBIs in 11½ seasons with the Royals.
"I had these three dates in Kansas City circled all season," Sweeney said.