To clear a place for Ka'aihue on the 40-man roster, the club recalled right-hander Joey Devine and placed him on the 60-day disabled list with a right rhomboid strain.
Ka'aihue started the season with the Royals but hit just .195 with two homers and six RBIs in 23 games. He was optioned to Triple-A Omaha, where he hit .272 with 65 RBIs in 95 games.
Ka'aihue was designated for assignment by the Royals on Sept. 21 after hitting .214 with two homers and eight RBIs in seven playoff games to help the Storm Chasers win the Pacific Coast League championship.
Hollingsworth spent most of the season with Double-A Midland before being promoted to Triple-A Sacramento on Aug. 27. He went 6-5 with one save and a 3.61 ERA over 17 appearances (16 starts) for Midland, and 1-0 with a 5.06 ERA in two starts for Sacramento.
Devine began the season with Sacramento, where he was 3-0 with three saves in 11 relief appearances. He didn't allow an earned run in 12 1/3 innings before being promoted to Oakland on May 20, where he was 1-1 with a 3.52 ERA in 26 appearances out of the bullpen. He was optioned back to Sacramento on July 27.