OAKLAND, Calif. — The Oakland A’s placed right-handed pitcher Ross Stripling on the 15-day injured list retroactive to Sept. 9 with a lower back strain and selected left-handed pitcher Kyle Muller from Triple-A Las Vegas, the club announced today. To clear a spot on the 40-man roster, the A’s designated left-handed pitcher Jack O’Loughlin for assignment.

Stripling began the season in the starting rotation and was 2-11 with a 5.72 ERA in 14 starts when he was moved to the bullpen on Aug. 14. He has no decisions and an 8.25 ERA in seven relief appearances and is 2-11 with a 6.08 ERA in 21 games overall. This is the second stint on the IL for Stripling this year as he was previously out from May 25 to July 24 with a strained right elbow.

Muller joins the A’s for the second time this season after going 0-1 with a 4.22 ERA and .749 opponents OPS in 18 relief appearances during his first stint. He pitched primarily in long relief as 13 of his 18 games were at least 2.0 innings, including six outings of 3.0 innings or more. The 26-year-old left-hander was on the A’s Opening Day roster, missed 36 games while on the injured list from May 27-July 6, and was designated for assignment on Aug. 13. Muller went 1-1 with a 4.43 ERA in four games, three starts, with Las Vegas after he was outrighted on Aug. 14, and is 1-2 with a 4.76 ERA in eight minor league appearances, including five starts, overall with the Aviators and Single-A Stockton.

O’Loughlin made his Major League debut with the A’s this year and compiled a 4.66 ERA in four relief appearances over two stints. He has spent the balance of the season with Las Vegas where he is 2-5 with a 6.19 ERA and .966 opponents OPS in 28 games, including 10 starts.