SEATTLE -- Garrett Richards’ road to a Major League mound in 2019 experienced a setback on Monday after the right-handed starter departed his fourth rehab assignment game with discomfort in his pitching shoulder.

The setback is unrelated to the Tommy John surgery that Richards underwent last July as a member of the Angels. He met with Padres doctors on Tuesday, and the hope is that this is simply a minor impediment.

“What I'm told from the doctors and trainers is anticipate this as a minor hiccup, that he feels ultimately pretty good today and they're all encouraged by the way he feels today,” Padres manager Andy Green said at T-Mobile Park, where the club opened a two-game series against the Mariners. “I don't know what that ultimately means. It's what you'd rather hear than the alternative right now.”

Richards had five strikeouts, two walks and two hits over 2 2/3 innings before departing after 51 pitches for Class A Advanced Lake Elsinore.

Richards has battled a glut of arm injuries throughout his eight-year career, including a biceps injury in ‘17 and the elbow issues that plagued him as far back as ’16, when he opted to treat the issue with stem-cell injections instead of Tommy John surgery. He’s never been on the injured list for a shoulder issue, however.

The Padres will give Richards a few days’ rest before reassessing next steps. Minor League rehab assignments for pitchers are capped at 30 days, though MLB allows extensions for pitchers returning from Tommy John.

“Our hope is that he moves forward and continues his rehab progression with a few days' delay,” Green said. “I don't know if that's the case yet.”

If and/or when Richards is activated, the Padres will have to clear a 40-man roster spot for him, though the club could certainly use him to eat innings for a young starting staff that will likely see its workload curbed over the final seven-plus weeks.

Richards signed a two-year, $15 million contract with San Diego, in a deal that was more about 2020 than ’19 and Richards bridging the gap to the Padres’ talented farm system, which remained No. 1 in the updated MLB Pipeline rankings that were revealed on Tuesday.

Over four outings with the Arizona League Padres and Lake Elsinore, Richards gave up eight runs (seven earned) and 11 hits, with 11 strikeouts and seven walks over 7 2/3 innings.

Castillo nearing return
Left-hander Jose Castillo (flexor strain in left elbow) threw a perfect eighth inning on Monday for Lake Elsinore with one strikeout, his 12th among the 17 batters he’s faced over his second rehab stint. Castillo was pitching for the second time in three days, which typically marks the penultimate step for a rehabbing reliever, preceding back-to-back days.

“That's as tight as we've gotten on him at this point in time and he felt really good, so we're all encouraged,” Green said. “If he continues on this path, the day of his return is getting close.”

Castillo was slated to be the Padres’ primary setup man and lefty specialist before sustaining his injury before the season started. He also experienced a setback during his first attempt at a rehab assignment in June.

Over 37 games last season, Castillo posted a 3.29 ERA and struck out 52 of the 150 batters he faced.

Players’ Weekend nicknames announced
Players’ Weekend will return from Aug. 23-25, when the Padres host the Red Sox for a three-game series, and on Monday, MLB revealed each player’s nickname that they will don on their jerseys during the third-annual event.

• Every team's Players' Weekend nicknames

Manny Machado was named San Diego’s Players’ Weekend ambassador, and the star third baseman will wear “El Ministro,” which is translated to “The Minister” and which he first began using after the 2017 World Baseball Classic.

• Shop for Padres Players' Weekend gear

Catcher Austin Hedges will sport emojis of a hedge and pig, with the hope that people will begin calling him “Hedgehog” instead of “Hedgy.” Twenty-year-old shortstop Fernando Tatis Jr. will, perhaps aptly, wear “El Niño,” while infielder Luis Urias will wear “Wicho,” which is a nickname for his first name. Right-hander Chris Paddack, who famously dresses in cowboy-esque attire on days he starts, will wear “Sherriff.”