NEW YORK – Major League Soccer Commissioner Don Garber called St. Louis and Sacramento, California, "front-runners" for the next round of expansion, which could occur as soon as 2020.

He said other candidates, in priority order, were Detroit; San Diego; San Antonio and Austin, Texas; and Cincinnati.

"What held us back in St. Louis for 20 years is we never had a viable stadium," Garber said Thursday during a meeting with the Associated Press Sports Editors. "Now we're talking to a group of investors and we're able to capitalize on the Rams have left. So there is a site where it's ready. ... St. Louis is a very, very high potential market, and one of the things that makes it more strategic for us is its proximity to Kansas City."

Garber visited California last week, and the Sacramento Republic of the third-tier United Soccer League released renderings of a proposed 25,000-seat stadium. The team also held a rally to show support.

"Sacramento is MLS ready," Garber said. "They've got 9,500 season tickets, good in any pro sports league. ... There's not a lot of competition there, and we seem to do better in those markets with less competition. There's an ownership group that's solid."

He said he told the Republic "the last piece of the puzzle" was for the team to obtain commercial commitments and sponsorships.

Garber said he received a call this week from Cincinnati FC owner Carl Lindner, whose team started play in the USL this season.

"He said, 'When can we come into MLS?'" Garber recounted. "I said, 'you've got to wait a while. We've been at this a few years. Just two good weekends doesn't necessarily mean you're going to have a sustainable fan base.'"

The league, which started play in 1996, currently has 20 teams, with Atlanta due to join in 2017 and a second Los Angeles team the following the year. Minneapolis-St. Paul also has been awarded a team and could open in 2017, and the league hopes David Beckham's tentative Miami team could start play in 2018.

Garber remains confident Beckham's group will finalize a stadium deal and said it is working to complete its investor group.

"If it doesn't happen, it would surprise us, if not shock us, that they weren't able to cross all the T's and dot the I's," he said.

Still, he added Miami and Los Angeles have "got to get busy fast" with stadium construction to meet deadlines. There were no significant updates on the search for stadium sites by New England and New York City.