Oakland, CA (SportsNetwork.com) - The Oakland Athletics placed reliever Sean Doolittle back on the 15-day disabled list with a left shoulder strain on Saturday.

Doolittle missed the first 1 1/2 months of the season with a strained rotator cuff. After five rehab appearances, the 2014 All-Star returned to Oakland's bullpen and pitched an inning on Wednesday before going back on the DL.

The left-hander had 22 saves and a 2.73 ERA in 61 appearances out of the bullpen in 2014.

To take Doolittle's spot on the 25-man roster, Oakland recalled right-hander Angel Castro from Triple-A Nashville. He had been optioned to the minors earlier in the week prior to Doolittle's activation.