ANAHEIM -- Garrett Richards' partially torn ulnar collateral ligament showed "progressive healing" in a followup MRI, while Andrew Heaney's "did not show the progressive healing that would've been optimal," Angels general manager Billy Eppler relayed to reporters on Monday afternoon.
As to whether the two frontline starting pitchers will ultimately need Tommy John surgery?
"Really hard to say," Eppler said. "In both cases, we were taking a conservative route. One case showed a little more progression than the other, but neither situation is at a point of decision-making at this point."
Richards will be re-evaluated in six weeks, which takes him all the way out to Aug. 8 without throwing a baseball. Heaney will be re-evaluated shortly after the All-Star break, in two to three weeks.
Richards, a 28-year-old right-hander, and Heaney, a 25-year-old left-hander, both underwent stem-cell therapy in hopes of avoiding an elbow-ligament replacement surgery that would knock them out until at least the start of the 2018 season.
The Angels haven't ruled either out for '16, but it's becoming increasingly clear that neither is likely to pitch this season. The hope is that stem-cell therapy can at least provide a normal offseason that will allow Richards and Heaney to be ready for the start of 2017.
The Angels haven't set a deadline with either pitcher, Eppler said, but added that a decision will not drag out to the point where they risk also missing a portion of the 2018 season if they ultimately opt for surgery.
"Organically, this is going to declare itself one way or the other," Eppler said, "before season's end."
Richards, eligible for free agency after the '18 season, and Heaney, controllable for five years after this one, opened as the Nos. 1 and 2 starters, respectively.
Heaney felt discomfort in his forearm during his first start, was promptly placed on the disabled list with a flexor muscle strain, then was shut down in the early stages of a throwing program and underwent stem-cell therapy on May 2. Richards left his sixth start, in Arlington on May 1, after 79 pitches because of what the club initially called dehydration and cramping, then underwent an MRI that revealed a high-grade tear of his UCL, prompting stem-cell therapy on May 16.
Both procedures were performed by Dr. Steve H. Yoon, out of the nearby Kerlan-Jobe Orthopaedic Clinic, who extracted stem cells from bone marrow and injected them directly into the damaged ligament.
Richards is "clinically asymptomatic of any issue," Eppler said, but Heaney has yet to make enough progress.
Richards and Heaney would both have to show they can throw competitively before the organization is comfortable ruling out Tommy John surgery.
"Clearly if they get to the point of picking up a baseball, throwing a baseball, going through the rehab protocol, going out on the rehab assignments, at that point, when they're competitively throwing pitches of consequence, they'll know," Eppler said. "That will be declared at that point in time."
Worth noting
• Mike Trout said he "hasn't thought about" whether he would like to compete in the T-Mobile Home Run Derby. Trout has yet to compete in the event, but has always sounded open to someday taking part. Trout said the new format, with timed rounds, "is more fun to watch. But I'm not sure."

• C.J. Wilson spent Monday getting a second opinion on his ailing left shoulder, which has bothered him while throwing off a mound since the start of Spring Training. Wilson had been throwing off a mound of late, but Eppler said: "It seems like it's not firing the way he wants it to fire."
• Tyler Skaggs, pitching in his first official game since April 20, completed 4 1/3 innings for Class A Advanced Inland Empire on Monday, giving up one run on five hits and no walks while striking out five. Skaggs threw his fastball 90-95 mph, sitting mostly at 93, in a 58-pitch outing.
• Eppler said conversations with the Angels' second-round pick, high-school outfielder Brandon Marsh, are "ongoing." Marsh is the only player taken within the top 10 rounds who has yet to sign and has a commitment to Kennesaw State University. The Angels have until July 15 to sign their picks.
• Angels setup man Joe Smith felt good while throwing an inning for Class A Advanced Inland Empire on Sunday, but only needed eight pitches to finish it. Smith, out since June 7 with a left hamstring strain, will make another rehab appearance on Wednesday and hopes to get activated by Friday.
• Third baseman Yunel Escobar missed his fourth straight game Monday because of a bone bruise in his left knee. Angels manager Mike Scioscia said Escobar is "making progress," but is still unsure when he'll return. Jefry Marte started in his place at third base, while Kole Calhoun led off again.
• The Angels added J.C. Ramirez to the active roster on Monday, optioning fellow right-handed reliever A.J. Achter to Triple-A to create room. Ramirez, 27, was claimed on waivers from the Reds on Sunday and has a 6.40 ERA in 27 appearances this season, striking out 28 batters in 32 1/3 innings.
"I personally think I need to be better because I have the stuff," Ramirez said. "I just haven't had the results yet."