SEATTLE -- Mariners right-hander Hisashi Iwakuma, one of the top starters in the American League the past three seasons, was placed on the 15-day disabled list on Friday with a strained lat muscle behind his right shoulder.
General manager Jack Zduriencik said the issue isn't believed to be serious, but Iwakuma felt some fatigue in his shoulder after his last start and will undergo an MRI on Friday night.
"We thought it was best to back him off and put him on the DL to give him time," Zduriencik said. "It's a long season and we don't want this to be an aggravated issue over the next 5 1/2 months. We'll know more after the MRI. At this point, we're hoping it's nothing more than shoulder fatigue and something very small."
Left-handed reliever Lucas Luetge was recalled from Triple-A Tacoma to temporarily fill Iwakuma's spot on the 25-man roster.
Iwakuma, 33, had gone 0-1 with a 6.61 ERA in his first three starts and was removed after just 71 pitches in his last outing, though he said he felt fine physically afterward even though his velocity has been down this year. He allowed four runs and five hits -- including a pair of solo home runs -- in 5 1/3 innings in that no-decision to the Astros on Monday and wasn't sharp in his first two starts against the Angels and Dodgers either.
Iwakuma had been scheduled to make his next start in Sunday afternoon's series finale against the Twins, but the decision to place him on the DL came after he played catch and continued to feel the same fatigue and stiffness prior to Friday's game at Safeco Field.
The move is retroactive to April 21, so he'll be eligible to return on May 6.
No announcement has been made on who will make Sunday's start, though left-hander Roenis Elias would be the logical choice to be recalled from Triple-A Tacoma. Elias last started on Monday for the Rainiers, so he'd be in line to start Sunday.
"We're not going to announce it until tomorrow, but I would say the obvious is the obvious," said Zduriencik, who wanted to wait until after Tacoma's game on Friday night to make the choice official.
Elias went 10-12 with a 3.85 ERA in 29 starts for Seattle as a rookie last season, but didn't make the rotation this spring and started the season in Tacoma. He's 2-0 with an 8.04 ERA in three starts for the Rainiers.
Iwakuma was 15-9 with a 3.52 ERA in 28 starts last season and 14-6 with a 2.66 ERA in 33 starts in 2013, when he was named to the American League All-Star team. After moving into the Mariners rotation on July 2, 2012, Iwakuma had the ninth-lowest ERA in the Majors at 2.97 from that point to the end of last season.
Over the last two seasons, Iwakuma's WHIP of 1.026 was the fifth lowest in the Majors among qualified starters, but that number was 1.408 in his first three games this season and he'd allowed five home runs in 16 1/3 innings.
Luetge presumably will be used to bolster the bullpen on a short-term basis until Elias is added. He's posted a 3.24 ERA in 8 1/3 innings over five appearances for Tacoma.
The Mariners rotation ranks 29th in the Major Leagues in starters ERA at 5.59 with Iwakuma and youngsters Taijuan Walker and James Paxton all struggling to start the year.
• Reliever Tom Wilhelmsen, who is on the 15-day disabled list with a hyperextended elbow, played catch on Friday for the first time since hurting his right arm on April 10. The 31-year-old will likely throw his first bullpen session next week when the team is in Houston, manager Lloyd McClendon said, as he works his way back.