The team announced the moves before Friday night's game against San Francisco.
Grandal had been on the DL since July 31 with a strained muscle on his right side. He played two games with Class-A Lake Elsinore on a rehab assignment and is hitting .312 with five home runs and 15 RBIs in 24 games with the Padres.
Hundley was placed on the DL retroactive to Thursday. He was batting .157 with three homers and 22 RBIs in 58 games with the Padres. He was optioned to Triple-A Tucson on June 30 and recalled Aug. 9.