Sports minister Hiroshi Hase said Friday he is concerned that there are more players involved in the baseball gambling scandal that has seen a fourth player from the Yomiuri Giants admitting to his involvement.

"I'd like to ask if he really is the last person involved. We can't clear those doubts," Hase said at a news conference following a Cabinet meeting. "I'd also like to ask Nippon Professional Baseball if it's just the Giants. I want this to be properly dealt with."

Giants reliever Kyosuke Takagi told his club Tuesday that he bet on baseball games in 2014. The admission followed the indefinite bans on three players from the team last November for getting involved in the same scheme.

Hase graduated from Seiryo High School in Ishikawa Prefecture, the same school as Takagi and former New York Yankee Hideki Matsui, and said he was saddened by the news.

"I've known him well since his high-school days, I was cheering him on watching games," Hase said of Takagi. "I feel sorry as one of the seniors from the same school.

"I want all those involved to be severely punished."

Olympic minister Toshiaki Endo said, "Fraudulent activities are inexcusable. It's important to squeeze all of the pus out."

Yomiuri on Friday confirmed that team chairman Tsunekazu Momoi and supreme adviser Tsuneo Watanabe have stepped down to accept responsibility.

Team owner Kojiro Shiraishi was replaced by Shoichi Oikawa, the executive adviser and senior deputy editor-in-chief of The Yomiuri Shimbun Holdings.

Lawyer and former public prosecutor Noboru Matsuda has also been installed as the deputy owner as he becomes the club's first-ever external director.