LOS ANGELES -- Dodgers right-hander Yoshinobu Yamamoto has a strained rotator cuff, manager Dave Roberts said Sunday, adding that tests did not show a tear.

The injury was initially described as triceps tightness before the strain was diagnosed. Yamamoto was placed on the 15-day injured list before Los Angeles beat Kansas City 3-0 on Sunday. He will not throw for a couple of weeks.

"It's just going to take time and rest. It's not season-ending," Roberts said.

Yamamoto, 25, playing his first year in the majors after departing his native Japan and signing a record $325 million, 12-year contract, is 6-2 with a 2.92 ERA.

"He's a guy that we're still trying to learn a lot about, and appreciate the fact that the most important time of the season is yet to come," Roberts said before the game. "His health is paramount. So for us to be proactive and put him on the IL seems like the smartest thing."

Yamamoto left Saturday's loss to Kansas City after two innings. He said through an interpreter after the game that his scheduled start the previous Thursday against Texas had been pushed back because of the tightness.

He also said the tightness was gone for most of Saturday, but he started feeling it again when he was warming up before the game.

Yamamoto threw two-hit ball over seven innings at the New York Yankees on June 7. He tossed 106 pitches, the fourth straight time he had thrown more than 100.

Roberts said he has been mindful of Yamamoto's pitch count, but also noted that Yamamoto was used to throwing 120 pitches or more when he pitched in Japan.

With Bobby Miller returning to the rotation for Wednesday's game at Colorado, the Dodgers will still have a five-man starting staff. Clayton Kershaw will also make his first rehab start this week.

Los Angeles' rotation went into Sunday's game with the majors' seventh-lowest ERA at 3.49.

The Dodgers also placed right-hander Michael Grove on the IL with a right intercostal strain. Right-handers J.P. Feyereisen and Michael Petersen were called up from Triple-A Oklahoma City. To make room for Petersen on the 40-man roster, right-hander Joe Kelly was transferred to the 60-day IL.

The Associated Press contributed to this story.