The Hokkaido Nippon Ham Fighters' Yuki Saito may need a month before returning to the rotation after the 22-year-old right-hander was diagnosed with a left abdominal strain on Monday.
An MRI revealed that the injury is expected to shelve Saito for two to three weeks, but according to chief trainer Yoshihiro Fukushima, the heralded rookie could be out longer.
"It's not as light as we thought it would be," Fukushima said.
"I want to be back as soon as possible," said Saito, who traveled with the team to Sendai for a three-game series against the Tohoku Rakuten Golden Eagles starting Tuesday.
"I can only do what I can right now, which is to try to get fit again."
Saito was taken out of Sunday's game against the Softbank Hawks after pitching one scoreless inning, when he complained of pain down his left side.
Saito is 2-0 in four starts this season for the first-place Fighters. Manager Masataka Nashida said Saito will make a rehab start in the minors before returning to the rotation.