Bass was designated for assignment on Monday when the Pirates reinstated starter Ross Ohlendorf from the 15-day disabled list.
During his two weeks with the big league club, Bass allowed nine earned runs on nine hits in 6 1/3 innings. He walked eight and struck out four. Bass is expected to pitch out of the bullpen for Indianapolis.
Other Minor League notes of interest:
Both Neil Walker and Pedro Alvarez went deep in Indianapolis' 8-1 win on Friday. The home run was Alvarez's ninth of the season, and his two-hit day bumped the third baseman's average this month up to .333. He has driven in 21 runs since the start of May. Walker still leads the International League in hits (46).
Right-hander Michael Crotta picked up the win for Indianapolis on Friday after allowing one earned run and seven hits in seven innings. The start was Crotta's third since being promoted from Double-A, and he went seven innings deep in all three. Since Indianapolis became affiliated with the Pirates in 2005, no Indians pitcher has pitched at least seven innings in each of his first three starts.