The Padres made the moves Saturday.
Hundley hit .166 with three home runs and 22 RBIs in 55 games this season. He struck out 50 times.
The Padres' second-round pick in 2005 has a career average of .277 with 33 home runs in 360 games.
This is the second call-up for the 23-year-old Grandal. He was promoted June 1 and was hitless in his only at-bat for the Padres on June 2. He was optioned back to Tucson on June 3, where he has hit .335 with six home runs and 35 RBIs in 56 games.