MLS has 20 clubs and four in the expansion process that will begin play over the next few years: Atlanta, Los Angeles, Minnesota and Miami. Along with Detroit, Sacramento and St. Louis have been reported as likely expansion cities.

Owners of the Los Angeles FC reportedly paid a $110 million expansion fee for their club, which begins play in 2018. Minnesota United FC, which begins play in 2017 or 2018, reportedly paid $100 million. New York City FC's ownership reportedly paid a $100 million expansion fee, while Orlando City FC's paid $70 million.

New York and Orlando began play last year, and future teams in addition to Minnesota and Los Angeles include Atlanta in 2017 and Miami once a stadium deal is formalized.

Gores and Gilbert — estimated to be worth $3.3 billion and $5.1 billion, respectively, by Forbes — announced their interest in owning an MLS team in Detroit in April at a news conference attended by MLS Commissioner Don Garber, who spoke glowingly about a team in this market.

The Gores-Gilbert group, which could eventually include other investors, said it wants to build a 500,000-square-foot soccer-specific stadium, which likely will seat around 24,000 and would cost $225 million to $250 million, on the 15 acres underneath the unfinished Wayne County jail project site — prime downtown real estate on Gratiot Avenue at I-375.

The $1 billion plan, designed by Detroit-based Rossetti Associates Inc., includes three 18- to 28-story glass towers along with retail, bars and restaurants.

The aim is to have a stadium open by 2020, but a major roadblock is that Wayne County owns the jail site and said last month it intends to complete the project. Work on the jail was halted in July 2013 because of a $100 million cost overrun.

Wayne County Executive Warren Evans has said he intends to work with the Gores-Gilbert group, but his priority is getting a justice complex built.

The Gores-Gilbert group still is focused on the jail site for a stadium, but is believed to be considering alternative locations.

"We believe the right development for that site is something that enhances the city and fuels the continued revitalization of Detroit," Matt Cullen, one of Gilbert's longtime top lieutenants and principal with his Rock Ventures LLC, said in a statement. "We remain committed to exploring an exciting and distinct large-scale development that will bring jobs, an increased tax base and substantial economic activity to our burgeoning urban core. And as such, we will continue working side by side with Wayne County throughout this process to ensure maximum positive benefit for the community."

Evans previously has said the two requirements for having the Gilbert-Gores project move forward are that Wayne County gets a new jail without additional cost to county taxpayers and that a reasonable offer for the site be received by the late summer or early fall, which is when he said the county expects to issue a request for qualifications to finish the project. The county reconfirmed this week the plans for an RFQ.

An MLS club, even at $200 million, is less expensive than the billionaires' other pro sports ventures: Gores bought the National Basketball Association's Detroit Pistons for $325 million in 2011, and Gilbert purchased the Cleveland Cavaliers for $375 million in 2005. The average MLS club is worth $157 million, according to the most recent valuations from Forbes.com, and the most valuable club was Seattle at $245 million.

The soccer league has a far lower barrier to entry than its U.S. major league counterparts. National Football League expansion is pegged at $1 billion, and the fee to relocate the St. Louis Rams to Los Angeles was $550 million this year.

MLS is a single-entity business, meaning all teams are owned by the league and all players are its employees rather than employed by the club. MLS pays the players. Team "owners" pay an investment fee to MLS for the right to operate a team in a geographic area. They become league shareholders rather than franchise owners. Teams keep their own books and budgets.

MLS has publicly said it continues to lose money — as much as $100 million annually.