The Athletics have designated left-hander Brad Mills for assignment, according to Ken Rosenthal of FOX Sports (on Twitter).

Oakland acquired Mills from the Brewers earlier this summer, and the southpaw made three starts for the defending AL West champs, pitching to a 4.41 ERA with a 14-to-7 K/BB ratio in 16 1/3 innings. He was excellent in 75 innings for Milwaukee’s Triple-A affiliate this season, pitching to a 1.56 ERA with 9.2 K/9 and 2.2 BB/9. Even with those strong numbers, he has a 4.19 ERA in 635 2/3 career Triple-A innings to go along with a 6.98 ERA in 69 2/3 big league frames.

Mills’ spot in the rotation was lost with this weekend’s blockbuster acquisition of both Jeff Samardzija and Jason Hammel from the Cubs, and his DFA will clear a 40-man roster spot for Hammel to be activated, MLB.com’s Jane Lee tweets.