ANAHEIM -- The Angels, already dealing with an assortment of injuries throughout their starting rotation, were dealt a debilitating blow on Friday, when it was revealed that their best starting pitcher, Garrett Richards, will likely require season-ending Tommy John surgery to repair a high-grade tear of his ulnar collateral ligament.

Richards will seek a second opinion, presumably from Dr. James Andrews, but Angels general manager Billy Eppler acknowledged that the invasive procedure, which would keep Richards out until at least the middle of the 2017 season, is "likely at this point."

"I'm disappointed," Richards said, "and you can't help but feel like you're letting your teammates down and kind of abandoning them in the middle of the season. I tried my best to kind of continue on and take the ball every fifth day and show up for my teammates and give us a chance to win. I'm just trying to kind of decompress right now and absorb what's going on, just figure out what the next step is in my recovery to getting back on the field."

Richards exited his Sunday start in Arlington after only 79 pitches with what the Angels initially deemed to be dehydration and cramping, then he skipped his between-starts bullpen session and indicated after Wednesday's game that he was dealing with general fatigue. But doctors found a tear in Richards' UCL on Thursday, prompting the team to scratch him from his scheduled Friday start against the Rays and replace him with long reliever Cory Rasmus.

"Sometimes pitchers feel a precise pain or can pinpoint a pain more, and he couldn't do that," Eppler said. "As he was talking to me, he just was not able to get his arm to fire. I've kind of known other pitchers that that's happened to, but it's more outside the ordinary. Usually guys can kind of point to an area, and he couldn't."

Andrew Heaney, who began the season as the Angels' No. 2 starter, also has a damaged UCL, as first reported by Jeff Passan of Yahoo! Sports.

Heaney received a platelet-rich plasma injection in his elbow late last week, one that will prevent him from throwing until at least the middle of June, and the Angels are hopeful that it will negate the need for Tommy John surgery. Eppler said "the findings from multiple doctors ranged from normal wear and tear consistent with age and usage, to some degree of tear" with Heaney, who is on the disabled list with what the team initially called a flexor muscle strain.

The Angels, Eppler said, are "opting for conservative care, like other pitchers have done."

Heaney -- not expected back until the start of July, at the earliest -- was transferred to the 60-day DL on Friday to create a 40-man-roster spot for relief pitcher Javy Guerra, who temporarily gives the Angels a nine-man bullpen. Guerra is taking the 25-man-roster spot of Richards, who was officially placed on the 15-day DL.

In other moves, left fielder Daniel Nava, previously nursing tendinitis in his left knee, was activated off the DL and fellow outfielder Rafael Ortega was optioned to Triple-A.

Richards was on his way to being one of the game's best pitchers in '14, winning 13 games and posting a 2.61 ERA in his first 26 starts, until he ruptured his left patellar tendon at Fenway Park in Boston on Aug. 20. He bounced back to have a strong '15 season, going 15-12 with a 3.65 ERA in 207 1/3 innings, and entered the '16 season as the Angels' Opening Day starter.

More than a year fully removed from knee surgery, Richards was confident he could take his game to another level this season. The 27-year-old right-hander already threw the hardest four-seam fastball among starting pitchers, backed it up with a wipeout slider and knee-buckling curve, and was excited about reintroducing his two-seam fastball with a more stable landing leg and incorporating a low-90s changeup that he finally began to grasp.

Richards made six starts, posting a 2.34 ERA while striking out 8.8 batters per nine innings, before his UCL gave out.

"I never threw one pitch that made me think, 'Oh my god, my arm is done,'" Richards said. "It was just kind of something that progressively snuck up on me and kept going. There was never one pitch where I felt anything specific."

The Angels' starting-pitching depth, which stood eight deep at the start of Spring Training, is now down to basically three, with Jered Weaver, Hector Santiago and Nick Tropeano remaining.

Tyler Skaggs, recovering from August '14 Tommy John surgery, hasn't been on a mound in about two weeks and was diagnosed with left biceps tendinitis, which will keep him from playing catch until at least the start of next week. C.J. Wilson, dealing with shoulder tendinitis, hasn't been on a mound since around the middle of March and won't start throwing bullpen sessions until next week at the earliest. Then there's Matt Shoemaker, who finished April with a 9.15 ERA and is currently in Triple-A.

Shoemaker, slated to start for Triple-A Salt Lake on Friday, will eventually rejoin the rotation. The Angels can also call up prospect Nate Smith, who has a 3.79 ERA in his first six Triple-A starts. Kyle Kendrick and Chris Jones, both acquired late in Spring Training, are also options in Triple-A.

Asked about searching for pitching help outside the organization, Eppler said: "I will look under every rock, inside and outside."

As for eventually having to trade Mike Trout, an outlandish idea tossed around on Friday?

"No chance," Eppler said. "You do not move superstar players."

The Angels were also among the teams who had a scouting presence at Tim Lincecum's showcase in Scottsdale, Ariz., on Friday. Lincecum, coming off hip surgery, was said to have looked strong, throwing his fastball in the low 90s, but would still need at least a month before being ready to join a Major League rotation. Kyle Lohse is still a free agent, John Danks is expected to be released by the White Sox after being designated for assignment, and Tommy Milone was recently placed on waivers by the Twins.

The Angels, who used starting-pitching prospects Sean Newcomb and Chris Ellis to acquire shortstop Andrelton Simmons from the Braves in the offseason, don't have the young talent that will allow them to acquire a front-line starting pitcher via trade.

"You're losing a front-line pitcher, no doubt about that," Eppler said of Richards. "This club, last year, showed a lot of fight. I kind of define mental toughness as being your best in all circumstances. This club has shown the ability to do that, and a lot of guys in that clubhouse, I don't think they back down from a fight."

Fantasy spin | Fred Zinkie (@FredZinkieMLB)

Fantasy owners should not panic over the loss of Richards. The righty logged a helpful 2.34 ERA across six starts this season. but he also posted a 1.33 WHIP after producing a 1.24 mark a year ago. And though Richards has been a useful fantasy asset since the outset of 2015 (3.46 ERA, 1.25 WHIP), he has not been a mixed-league ace. When searching for a Richards replacement, owners will need to look outside the Angels' organization. J.A. Happ, Jerad Eickhoff, A.J. Griffin and Chris Tillman -- all on waivers in many leagues -- represent strong options. Those in deep formats can consider adding the likes of Brandon Finnegan, Jesse Hahn or Nathan Karns. Owners may also opt to use Richards' roster spot to stash a Minor Leaguer with massive upside, such as Tyler Glasnow or Blake Snell.

Alden Gonzalez has covered the Angels for MLB.com since 2012. Follow him on Twitter @Alden_Gonzalez and Facebook , and listen to his podcast. Abbey Mastracco contributed to this story.