OAKLAND, Calif. -- The Oakland Athletics activated left-hander Richard Lovelady from the 15-day injured list before Sunday's game against the Chicago White Sox.

Last-place Oakland also optioned lefty Kyle Muller to Triple-A Las Vegas. The 25-year-old Muller is 1-4 with a 7.79 ERA in 11 starts this season.

Lovelady had been sidelined by a strained left elbow. He pitched a scoreless inning against Tampa Bay on June 15 before departing with the injury.

"The way he walked off the mound, we were all concerned with whether or not he would be back with us this year," manager Mark Kotsay said. "So, getting him back, it's great for him individually that there wasn't anything severe in the injury."

Lovelady made one rehab appearance at Single-A Stockton on Friday, allowing one run in one inning. The 27-year-old pitcher went 0-3 with a 3.86 ERA in 24 relief outings for the A's before the injury.

"He had some success with us and we're hoping he gets back in here and continues to perform the way he did before the injury," Kotsay said.

Muller pitched five innings Saturday against the White Sox after he was recalled from the minors, allowing three runs and six hits. He did not factor into the decision as Oakland won 7-6 in 10 innings.

Muller was Oakland's Opening Day starter. The 25-year-old has struck out 37 and walked 27 in 52 innings.

"I think the next step is pitching deeper into games, limiting the pitch count, getting early-count outs with the changeup, establishing a changeup that he can command in the zone," Kotsay said. "Those are development steps that he needs to kind of grow in to be able to be a sustainable big league pitcher, really."

Muller, a second-round pick in the 2016 amateur draft, was acquired from Atlanta in a three-team trade in December. He is 4-9 with a 6.50 ERA in parts of three major league seasons.