Any financial transactions between umpires and club employees are strictly prohibited. Choi retired from umpiring in 2014.

According to the source, Lee was grilled by the prosecutors on Tuesday and was questioned whether there was a money transaction between him and Choi. Lee, who is currently indicted on charges of fraud and embezzlement in a separate case, denied such allegations against him.

On Wednesday, the prosecutors requested an arrest warrant for Choi on charges of fraud and habitual gambling. According to the prosecutors, Choi borrowed some 30 million won from baseball officials and his friends but didn't pay them back. The prosecutors, however, have yet to confirm whether he was involved in a match-fixing scheme.

When media reports first began alleging illicit transactions between Choi and KBO clubs last year, the league office conducted its own investigation into the matter. At the time, the Heroes told the KBO that Choi approached them for cash but they did not give him any money.

South Korea's sports ministry, meanwhile, has requested a prosecution probe into the KBO for its suspected negligence of duty in handling the recent money scandal. The ministry said its own preliminary investigation revealed that the KBO became aware of Choi's malpractice in August 2016, but launched its internal probe into the case six months later. (Yonhap)