LAS VEGAS- MGM Mirage said on Wednesday its outgoing chairman and chief executive is leaving its board, severing all formal ties with the casino operator he led for more than 13 years as he faces increased scrutiny over whether he misrepresented his academic credentials.

Mr Terrence Lanni will step down from the board of directors when he officially retires from the company on Sunday, MGM Mirage said in a filing with the Securities and Exchange Commission.

Mr Lanni, 65, abruptly announced his retirement as CEO earlier this month but said he planned to remain on the board of directors. But questions arose after the University of Southern California disclosed Mr Lanni had not received a master's degree in business, as he had long claimed.

MGM Mirage spokesman Alan Feldman said Mr Lanni did not mention the degree flap when he told company executives of his decision to leave the board, saying only that he and his wife wanted to devote more time to their philanthropic work.

When asked whether questions about Mr Lanni's academic credentials played into the decision, Mr Feldman said: 'I would think that a man who's been continuously licensed for 32 years and whose contributions to the industry are of such high regard, that I can't imagine anyone would have taken seriously an inquiry about this,' he said.

Mr Lanni's corporate biography has long held that he earned a master's degree in business from USC. A university spokesman said Mr Lanni took classes toward the degree from 1965 to 1967, but never graduated.

If regulators found Mr Lanni submitted false information on his license applications, he could have been denied a spot on the board.

It was not clear whether Mr Lanni claimed the degree as part of gambling license applications submitted to regulators where MGM Mirage operates casinos.

Regulators in Nevada and Mississippi said the contents of Mr Lanni's application were private. An Illinois regulator said Mr Lanni was not required by that state to have a gambling license.

Mr Eric Bush, administrative manager for the Michigan Gaming Control Board, told wires agencies that the state's gambling license application does not require applicants to list their educational background, but regulators were investigating that matter anyway.

Mr Lanni, who received US$9.6 million (S$14.5 million) in compensation in 2007, led MGM Mirage from a one-casino operation to its current position as the largest casino-operator on the Las Vegas Strip.

MGM Mirage owns and operates 17 properties in Nevada, Mississippi and Michigan, and has 50 per cent investments in four other properties. -- AFP