Celtic's Japanese pair suffer injuries
"I've had pain from my groin, an ankle and a calf since the end of last season," he said. "The calf and ankle have been getting better in recent weeks.
"While I was playing for Japan, I took pain-relieving medicine. But it got worse."
The January transfer window signing said he picked up a knee injury during a reserves clash with Gretnas last season.
"It's got so bad I can't play any longer," he said.