Seattle Mariners right-hander Hisashi Iwakuma has a strained tendon in the middle finger of his throwing hand that will sideline him for four to six weeks.

Iwakuma was injured while working out at home in January in southern California, the Tacoma News Tribune reported Thursday.

"I knew it was injured. I didn't think it was a major thing," Iwakuma said through a translator. "I rested my finger for about a week and started playing catch again, long toss. I thought it was good, but then the pain didn't go away."

No surgery is necessary, but Iwakuma will not be able to throw for at least three weeks and is likely to miss all of spring training, leaving his status in doubt for Opening Day. The finger is scheduled to be re-examined in three weeks.

"To be honest, very disappointed with what happened," Iwakuma said. "We have to go from here on."

Last season, Iwakuma finished third in the American League Cy Young Award voting after posting a 14-6 record with a 2.66 ERA, 42 walks and 185 strikeouts in 220 innings. His ERA was the third lowest in the AL.

"Luckily, this does not appear to be a serious injury," Mariners general manager Jack Zduriencik said in a statement. "It is a setback for 'Kuma,' but we are confident that he will quickly overcome the missed time and be able to rejoin our rotation early in the regular season."