Yamamoto was undergoing further medical testing on Sunday, the results of which were not immediately available. The hope among the Dodgers is that the injury isn’t serious, but Houston Astros pitcher Justin Verlander experienced similar triceps tightness before undergoing Tommy John surgery in 2020.

“Right now, as I sit here, no, I don’t think so,” manager Dave Roberts, speaking before Sunday’s series finale against the Kansas City Royals, said when asked if the injury could be a precursor to something more serious.

“And I think that he was smart enough to notify us when there was some tightness in his triceps. We’ll know more with the testing and him talking to the doctors, but I don’t think so. I really don’t.”

Yamamoto allowed only one hit Saturday night, but there was a noticeable dip in the velocity of the 28 pitches he threw. His four-seam fastball ranged from 92.9 mph and 95.9 mph with an average of 94.2 mph, down 1.3 mph from his season average of 95.5 mph entering the game.

Yamamoto threw 29 pitches that were clocked at 97 mph or higher in his previous start in which he blanked the New York Yankees on two hits over seven innings on June 7. The velocity of his secondary pitches were also down Saturday, his curve by 2.4 mph and his split-fingered fastball by 2.9 mph.

“The most important time of the season is yet to come, and his health is paramount,” Roberts said. “So for us to be proactive and put him on the IL, kind of reset him, seems like the smartest thing to do.”

Yamamoto, whose durability and dominance during his seven years in Japan were two of the reasons the Dodgers signed the 25-year-old to a 12-year, $325-million deal in December, said through his interpreter that he began feeling tightness in his triceps last week, as he was recovering from his Yankee Stadium gem.

“That was the reason” his scheduled Thursday night start against the Texas Rangers was pushed back to Saturday night against the Royals, Yamamoto said.

Yamamoto completed his between-starts workout in the bullpen on Thursday and said he was not experiencing any triceps tightness on Saturday. The discomfort flared up during pregame warmups, but Yamamoto said “it was not that serious at that point. … Then, as I was pitching [in the game], it started [to get worse].”

There was some confusion after the game, with Yamamoto telling reporters that he informed pitching coaches Mark Prior and Connor McGuiness that he felt some discomfort while warming up and Roberts saying that he “didn’t know until the second inning that [Yamamoto] couldn’t go back out there for the third inning.”

Roberts said he gained some clarity on the situation later Saturday night.

“I did talk to Mark, and the conversation [with Yamamoto] was, ‘How do you feel?” Roberts said. “And [Yamamoto said], ‘I don’t feel 100%. I don’t feel frisky, but I feel fine.’

“There are many conversations that happen every day in the big leagues with the pitching coach, where you’re not going to expect to feel frisky every start and you get through it. So again, that’s the communication that was relayed to me. … I still stand by the fact that I wouldn’t put a guy out there in harm’s way. I’ve never done it.”

Though the Dodgers will be losing one of their best pitchers for at least two weeks, one who is 6-2 with a 2.92 ERA in 14 starts and has struck out 84 batters and walked only 17 in 74 innings, Yamamoto’s injury won’t leave a gaping hole in the rotation.

That’s because Bobby Miller is scheduled to return from a two-month absence because of shoulder inflammation to start Wednesday night’s game at Colorado, eliminating the need for the Dodgers to employ a six-man rotation. The Dodgers also expect erstwhile ace Clayton Kershaw to return from shoulder surgery in mid-July.

“Part of constructing the roster is getting an abundance of starting pitching,” Roberts said. “Everywhere in baseball, guys go down at different times, and you’ve got to be able to backfill. To know we’re getting Bobby back and Clayton is starting a rehab assignment [this week] is certainly helpful.”

Yamamoto wasn’t the only Dodgers right-hander to be sidelined. Reliever Michael Grove was placed on the 15-day IL because of a right intercostal muscle strain, an injury that is not expected to sideline the right-hander for more than a few weeks.

To replace Yamamoto and Grove on the roster, the Dodgers recalled relievers J.P. Feyereisen and Michael Peterson, both 31-year-old right-handers, from triple-A Oklahoma City.

Peterson, whose fastball touches 98 mph, had a 1.31 ERA and 31 strikeouts in 22 ⅓ innings of 23 triple-A games. Originally drafted by the Milwaukee Brewers in the 17th round in 2015, Peterson has yet to pitch in the big leagues.

Saturday night’s game turned on an epic 12-pitch battle in the top of the sixth inning between Dodgers reliever Blake Treinen and Royals left fielder MJ Melendez, who fouled off six two-strike pitches and took a ball to work the count full.

Melendez then drove the 12th pitch of the at-bat over the wall in right field for a grand slam that turned a 2-1 deficit into a 5-2 Kansas City lead.

The Dodgers had taken a 2-1 lead in the fourth inning when Gavin Lux grounded a bases-loaded, two-out, two-run single to center field.

Dodgers right-hander Yohan Ramirez retired the side in order in the fifth, and Treinen, who returned from a shoulder injury to open his season with 14 scoreless appearances in which he struck out 19 and walked only two in 13 innings, took over in the sixth.

The veteran right-hander got Bobby Witt Jr. to fly out to the warning track in left for the first out but uncharacteristically walked the next three batters, prompting a visit from Roberts.

Treinen struck out pinch-hitter Adam Frazier with a wicked 83-mph slider, but he could not retire the stubborn Melendez, who boosted Treinen’s ERA from 0.00 to 2.63 with his game-turning slam.

Treinen didn’t have usual command of his slider, so nine of the pitches he threw to Melendez were cut-fastballs.

“The cutter was probably the pitch I had the most feel for tonight, but it also handcuffed me because I can’t keep throwing the same pitch over and over again to anybody in this league,” Treinen said.

“The biggest thing was just the walks. When I walk people, they make you pay. You can live with solo shots, you can live with a couple knocks, but when you give up three bases, it’s a frustrating one from that perspective.”