Former Oxford City director Thomas Guerriero has pleaded guilty to running a $6.6 million telemarketing and investment fraud conspiracy.

Guerriero, 39, of Hillsboro Beach, South Florida, resigned from his role as director of Oxford City FC in December due to "ill health" - just before he was indicted on federal charges in December.

The club said at the time it had no knowledge of Guerriero's business dealings in the United States.

Guerriero pleaded guilty yesterday to one count of conspiring to commit mail and wire fraud in the federal court in Miami, according to the Sun Sentinel newspaper.

The maximum penalty for the offence is 20 years in federal prison.

He has agreed to pay $6.6 million in restitution and forfeit homes he owns on the Hillsboro Mile, in Boca Raton and Deerfield Beach, as part of the plea agreement.

Prosecutors are expected to dismiss the other charges — including witness-tampering and obstruction of justice — after United States District Judge Beth Bloom sentences him on May 13.

Investigators said Guerriero was the ringleader of the fraud, based in Deerfield Beach.

Eight people from Broward and Palm Beach counties were indicted with him.

Guerriero, who lived on the Hillsboro Mile and said he has a graduate degree in business studies from Harvard University, came up with the idea for the fraud and wrote scripts his sales team used to get about 150 people from all over the United States to invest, prosecutors said.

Guerriero came under investigation by the FBI and the United States Securities and Exchange Commission last year.

He has been jailed since December and his assets have been frozen in a civil court action filed by the SEC.

Investigators said the fraud operated from July 2013 to July 2015 and affected more than 150 victims from all over the United States who bought stock.

The suspects are accused of lying to investors about the "safety, profitability, and transferability" of the stock and the commissions and fees being paid.

Telemarketing sales agents claimed the company owned $90 million worth of real estate, the Oxford City Football Club team in Texas and an online university with 10,000 students that would bring in as much as $100 million.