The operation, which will happen later this month, likely will keep him from pitching again until 2020.
Richards, 30, was placed on the 10-day disabled list on Wednesday after an MRI exam revealed damage to his right UCL. He exited Tuesday's start against the Seattle Mariners in the third inning with what the team called forearm irritation.
In other Angels news, the team activated left-hander Tyler Skaggs from the DL and optioned right-hander Jaime Barria to Class-A Inland Empire.
--In an effort to improve his on-field durability, New York Mets outfielder Yoenis Cespedes has been taking groundballs at first base while rehabbing in Port St. Lucie, Fla., according to multiple reports.
Cespedes reportedly is willing to move to the position and will continue to get reps there as he ramps up baseball activities. The 32-year-old has played only in the outfield, primarily left field in recent seasons, during his major league career.
Cespedes has been out since May 13 with a strained right hip flexor, and he also is battling a chronic heel injury. He has played just 37 games this season after being limited to 81 last year because of hamstring injuries. In the second year of a four-year, $110 million contract, Cespedes is hitting .255 with eight home runs and 28 RBIs this year.
--The Minnesota Twins placed struggling slugger Logan Morrison on the 10-day disabled list due to a left hip impingement. Shortstop Ehire Adrianza was reinstated from the disabled list in a corresponding move.
Morrison went 1-for-5 with his 11th home run of the season in playing all nine innings of the Twins' 8-5 win over the Kansas City Royals on Wednesday. Morrison, who has been bothered by the hip injury in recent weeks, is hitting .193 in 80 games this season, splitting time between first base and designated hitter.
Adrianza returns from a minimum-length stint on the DL with a left hamstring strain. The 28-year-old has hit .261 with four home runs and 19 RBIs in 64 games with the Twins this season.
--The Arizona Diamondbacks placed pitchers Shelby Miller (right elbow inflammation) and T.J. McFarland (left neck strain) on the 10-day disabled list. In corresponding moves, the team recalled right-handers Matt Koch and Silvino Bracho from Triple-A Reno.
Miller, 27, started Wednesday night's 19-2 loss in Colorado and pitched just one inning, giving up five runs on four hits and two walks, before being removed due to right elbow tightness. He had Tommy John surgery in May 2017 and was activated off the disabled on June 25.
In other Diamondbacks news, the National League has added right-hander Zack Greinke to the All-Star team, replacing Chicago Cubs lefty Jon Lester, who will pitch Sunday and opted to be ineligible for the game as a result.
--The Boston Red Sox placed third baseman Rafael Devers on the 10-day disabled list, retroactive to July 11, with left shoulder inflammation. He sat out Boston's game against Texas on Wednesday night as a result of the injury.
The Red Sox recalled infielder Tzu-Wei Lin from Triple-A Pawtucket to replace Devers on the roster.
Devers, 21, has appeared in all but five of Boston's 94 games and is batting .241 with 14 home runs and 48 RBIs. Lin, 24, hit .162 in 16 games with the Red Sox earlier this season.
--The Oakland A's activated right-handed pitcher Trevor Cahill from the 10-day disabled list, optioning right-hander Chris Bassitt to Triple-A Nashville to make room on the roster.
A strained right Achilles forced Cahill, 30, to miss 27 games. On the season, he is 1-2 with a 3.08 ERA in eight starts after beginning the season in Nashville. Bassitt, 29, pitched 32 innings for Oakland this season, going 2-3 with a 3.38 ERA. He got the win Wednesday at Houston, pitching five innings of three-run ball.
--Field Level Media