Tohoku Rakuten Golden Eagles manager Senichi Hoshino, who is taking time off due to lower back pain, has been diagnosed with a lumbar herniated disk and a serious disease that causes compression of the spinal nerve roots, the team announced on Tuesday.

The ailment Hoshino, 67, suffers from affects his thoracic vertebrae and is known medically as ossification of the ligamentum flavum. This condition has resulted in the hardening of the ligaments near his spine.

Eagles team president Yozo Tachibana, answering reporters’ questions Tuesday at the team’s training facility in Tokyo, said, “The manager’s health is paramount. I would like for him to return when he is healthy.”

It is uncertain whether Hoshino will undergo surgery, but he is likely to be sidelined for the foreseeable future. Pitching coach Yoshinori Sato will serve as acting manager in Hoshino’s place for the time being.

“I have to apologize. I’m uncertain (whether to have surgery),” said Hoshino.

Hoshino began complaining of pain in his lower back after a game on Sunday. He took the day off for Monday’s game against the Tokyo Yakult Swallows, following an examination at a Tokyo hospital.

Hoshino, who led Rakuten to its first Japan Series championship in its ninth year last season but whose team this year trails in fifth in the Pacific League, has been experiencing back pain for some time and he has been taking painkillers to battle through.

But he said the pain has become too much to bear.

“It has grown since before. It’s come to the point where I can’t fake it anymore,” said Hoshino, whose condition makes it difficult for him to even walk. “If I just ignore (the condition) and later were to hear that it progressed, I get the feeling I should take care of it now. I am determined to make a comeback.”

The Ministry of Health, Labor and Welfare designates ossification of the ligamentum flavum as an incurable disease. Yomiuri Giants right-hander Daisuke Ochi and Fukuoka Softbank Hawks lefty Kenji Otonari have both undergone surgery to treat the ailment.