Dodgers’ Yoshinobu Yamamoto likely will be placed on injured list

A noticeable drop in the velocity of his four-seam fastball in the first inning was the first sign that something was not right with Dodgers right-hander Yoshinobu Yamamoto on Saturday night.

The red lights then began flashing after the top of the second, when SportsNet LA cameras caught pitching coach Mark Prior hurriedly summoning manager Dave Roberts and an athletic trainer into the tunnel below the dugout and reliever Michael Grove began warming in the bullpen.

Sure enough, Yamamoto was pulled after giving up one hit in two scoreless innings of an eventual 7-2 loss to the Kansas City Royals in front of a crowd of 50,423 at Dodger Stadium, the team announcing an initial diagnosis of triceps tightness.

After the game, Roberts said there was a “high probability” Yamamoto would be put on the 15-day injured list. The Dodgers will make a decision after he is evaluated Sunday.

Yamamoto, a former Nippon Pacific League star who signed a 12-year, $325-million deal with the Dodgers in December, was originally scheduled to start Thursday night’s series finale against the Texas Rangers.

But after playing catch in the outfield under the watchful eyes of general manager Brandon Gomes and several members of the training staff last Tuesday afternoon, Yamamoto did not proceed to the bullpen to throw a between-starts session.

Gomes spent 10-15 minutes in the outfield talking to Joel Wolfe, Yamamoto’s agent. The next day, the Dodgers announced Yamamoto’s start would be pushed back to Saturday to give him two extra days of rest after he threw a season-high 106 pitches while throwing seven shutout innings on two hits against the New York Yankees on June 7.

Yamamoto, who entered Saturday with a 6-2 record and 3.00 ERA in 13 starts, walked one in a scoreless first inning against the Royals and gave up an infield single in a scoreless second, but his 12 four-seam fastballs were clocked between 92.9 mph and 95.9 mph, with an average of 94.2 mph.

His 28th and final pitch of the night was a 93.3-mph fastball that struck out MJ Melendez.

Yamamoto, 25, threw 29 pitches that were clocked at 97 mph or higher in that June 7 start at Yankee Stadium, which he attributed to “my mechanics working very well.” He had thrown three pitches above 97 mph all season before that game.

His four-seamer Saturday was down 1.3 mph from its season average of 95.5 mph. The velocity of Yamamoto’s secondary pitches were also down, his curveball by 2.4 mph and his split-fingered fastball by 2.9 mph.

Dodgers pitcher Yoshinobu Yamamoto delivers in the first inning Saturday.

(Gina Ferazzi / Los Angeles Times)

“We tried to give him an extra day just to kind of get off that high [from his Yankee Stadium start] and be able to reset back here at Dodger Stadium,” Roberts said before Saturday’s game, “but he feels good physically.”

If Yamamoto is put on the 15-day injured list, he would be replaced in the rotation by right-hander Bobby Miller, who is scheduled to start Wednesday night at Colorado after sitting out two months because of shoulder inflammation.

Saturday’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 for a full count.

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.

Kansas City’s Garrett Hampson taps teammate MJ Melendez on the helmet after Melendez hit a grand slam off Dodgers pitcher Blake Treinen in the sixth inning Saturday.

(Gina Ferazzi / Los Angeles Times)

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 mound 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.

The Royals added two insurance runs off left-hander Anthony Banda in the seventh for a 7-2 lead, Garrett Hampson sparking the rally with a leadoff triple and Witt (single) and Nelson Velasquez (sacrifice fly) driving in the runs.

Seth Lugo, a veteran right-hander who signed a three-year, $45-million deal with Kansas City last winter, gave up two runs and six hits in six innings, striking out four and walking one, to improve to 10-2 with a 2.40 ERA.

Max for the minimum

Max Muncy’s recovery from a right rib-cage strain will stretch into a second month. The third baseman, who went on the injured list on May 17, is fielding ground balls, throwing and running, but he won’t swing a bat for at least another week.

“Honestly, I don’t know what his timeline is,” Roberts said, “but it’s even slower than I think we all expected.”

Muncy was batting .223 with a .798 on-base-plus-slugging percentage, nine homers and 28 RBIs in 40 games when he got hurt. He thought he would return in two or three weeks but felt a “twinge” in his rib cage while taking batting practice in Arizona in late May and has been unable to resume swinging a bat.