Rainey's contract was selected from Triple-A Louisville on Tuesday.
Rainey has just two innings under his belt at the Triple-A level, but he hasn't allowed a run and holds a 5:1 K:BB. He also drew raves reviews from manager Bryan Price during spring training, so it's not surprising to see him in the big leagues already. He should slot into lower-leverage situations to start, but it's not crazy to think he could find his way into high-leverage situations if he finds success in the majors. Yovani Gallardo was designated for assignment to make room for him on the active roster.