Koehler announced his retirement on his personal Twitter feed Monday.

Koehler was placed on Double-A Altoona's 7-day injured list Aug. 18 due to a right shoulder strain, Jason Mackey of the Pittsburgh Post-Gazette reports.

Koehler (shoulder) was activated from the 7-day injured list and assigned to Double-A Altoona on Tuesday, Rob Biertempfel of The Athletic reports.

Koehler (shoulder) made a rehab appearance Tuesday for the Pirates' rookie-level Gulf Coast League affiliate, retiring two of the batters he faced and yielding two runs on two hits.

Koehler (shoulder) signed a minor-league contract with the Pirates on Wednesday, Rob Biertempfel of The Athletic reports.

Koehler underwent season-ending shoulder surgery Tuesday, Andy McCullough of the Los Angeles Times reports.

Koehler (shoulder) has been throwing bullpen sessions and is scheduled to face hitters in the upcoming days, but hasn't been progressing in his recovery as quickly as the Dodgers hoped, Bill Plunkett of The Orange County Register reports. "The curveball has been good, the fastball velocity has been good," manager Dave Roberts said of Koehler. "As I understand it, when he throws a 'pen, to kind of recover and be able to bounce back and do the same thing again [is a problem]."

Koehler (shoulder) suffered a setback during rehab Sunday, J.P. Hoornstra of the Los Angeles Daily News reports.

Koehler (shoulder) could rejoin the Dodgers before the All-Star break, Andy McCullough of the Los Angeles Times reports.

Koehler (shoulder) has progressed to throwing off flat ground from 75 feet, the Associated Press reports.