Dodgers reliever Tom Koehler undergoes season-ending shoulder surgery

Tom Koehler, the right-handed reliever signed by the Dodgers last winter as a potential replacement for setup man Brandon Morrow, underwent season-ending surgery on his right shoulder, manager Dave Roberts said. The operation probably will end Koehler’s tenure with the organization without him ever throwing a pitch for the team.

Koehler was diagnosed with a strained anterior capsule after appearing in a spring-training game at Camelback Ranch on March 2. The Dodgers did not place a timetable for his return, but retained hope that he could come back. Those hopes were dashed when Koehler felt “a little something a few days ago which didn’t fit the progression of his rehab,” Roberts said.

The Dodgers signed Koehler, 32, to a $2-million contract with another $2 million in incentives. Koehler will not reach those incentives.

“He was a guy who when we signed him this winter, we were all excited about it,” Roberts said. “Disappointing for him, for our ballclub, because I do think that he could have added a good element to our ‘pen.”

Buehler to be activated Wednesday

Walker Buehler will be recalled from the minors to start Wednesday against the Phillies. Buehler has not pitched in a game since July 13. The team will carry six starting pitchers with Buehler active.

“The plan is for Walker to stick around a little bit,” Roberts said.

The Dodgers do not have a day off until Aug. 6, and can use a six-man rotation to keep their arms fresh.

Baez back Thursday; Ryu to start rehab soon

Pedro Baez collected four outs for double-A Tulsa on Monday and is expected to rejoin the Dodgers on Wednesday, with the team desperate for arms after Tuesday’s 16-inning loss.

Josh Fields (shoulder inflammation) is “still a little bit behind,” while Tony Cingrani (shoulder discomfort) “is moving forward,” Roberts said.

The Dodgers are hoping their relievers return to full health as they scan the trade market for other options before the July 31 deadline.

Hyun-Jin Ryu (torn groin muscle) could begin a minor league rehab assignment this week. Ryu posted a 2.12 ERA in six starts before injuring himself May 1. He will require at least four outings to build up his pitch count, Roberts said. The organization does not view Ryu as an option for a relief role, given the maintenance required to heat up his surgically repaired shoulder.

“We’re excited that he’s making his way back,” Roberts said.

andy.mccullough@latimes.com

Twitter: @McCulloughTimes