Rocco Commisso has extended his deadline for the U.S. Soccer Federation to consider his offer to invest $500 million in a revamped North American Soccer League.

Commisso told ESPN FC the new deadline is May 31, after originally giving U.S. Soccer until May 21 "to engage in sustained direct negotiations through representatives empowered to make a deal." He added that, as of Wednesday morning, the USSF has not responded to his "latest communication."

Commisso first presented his offer to the USSF in a letter dated April 13, one that asks the federation to grant the NASL a 10-year "runway" to allow the league to come into compliance with the USSF's Professional League Standards -- which specify among other things a minimum number of teams -- as well as allow an owner in the revamped league to own multiple teams. Commisso's proposal also requested that the USSF make significant changes in terms of how it governs the sport.

In a bid to start the league in 2019, Commisso has been keen to present his plan to the USSF, but getting the two sides to the negotiating table has proved to be a challenge.

Commisso canceled a May 9 meeting in Chicago amid concerns that independent members of the USSF Board of Directors wouldn't be present. He also felt he could not obtain assurances from the USSF that details of his plans wouldn't be leaked to MLS and the USL, the latter of whom has previously been a competitor of the NASL.

The USSF has long contended that it wants a meeting to take place, but prefers to see more details of Commisso's plan prior to meeting. A USSF spokesperson said via text message, "We remain open to a meeting."

According to Commisso, the USSF has informed him that it is not possible for the full Board of Directors to consider his proposal before the June 13 vote in which the FIFA Congress will award the hosting rights for the 2026 World Cup. The USSF is part of the United Bid that consists of the U.S., Mexico, and Canada. Morocco is the other contender. With USSF president Carlos Cordeiro focused on the bid, Commisso extended his deadline.

Larry Busacca/Getty Images

In setting the new deadline, Commisso has asked the USSF to provide "a list of interim meetings and actions that it believes are prerequisites for a final board meeting at which a 'yes or no' decision on the proposal will be made" with a final Board meeting to be held no later than June 29.

"I've lost already $18 million," Commisso said. "I'm not going to invest more money unless I know that after I invest, someone isn't going to pull the rug out from under me. I'm just not going to do it. So I need certainty. If we fail that's our problem. But we're not going to go out and put hundreds of millions of dollars at risk here."

The NASL has been locked in a dispute with the USSF since last September, when the federation decided to deny the league a Division II sanction. The NASL has since filed two separate lawsuits, one against the USSF alleging anti-trust violations, and another against nearly every member of the USSF Board of Directors, alleging a breach of fiduciary duties.

In the interim, the NASL canceled its 2018 season, with the Cosmos, Miami FC, and the Jacksonville Armada competing in the National Premier Soccer League -- unofficially the fourth tier.

In the meantime, a few more details of Commisso's plan have emerged. The plan calls for the league to have at least 10 teams for the 2019 season, and aims to obtain Division I sanctioning for the 2020 season with a minimum of 14 teams. Commisso says a total of 12 markets have already been identified, and include former NASL sides New York, Jacksonville, Miami and Puerto Rico as well as current NPSL teams in Hartford, Detroit and Chattanooga.

"In Chattanooga, we're interested in [a league] that looks more like the rest of the world works, that won't stick us in a lower tier for perpetuity," said Chattanooga FC owner Tim Kelly. "We want a system that is at least moving towards [promotion and relegation]. Anything that looks like that and will give us 25-30 games a year, we're going to be in for."

The $500m in funding includes $250m from Commisso with Jacksonville owner Robert Palmer and Miami FC owner Riccardo Silva contributing a total of $50m. Commisso said "leading Wall St. banks" are prepared to assist in the completion of the fundraising. The funding will be made available to teams over a 10-year period, and will primarily be used operations and stadium expenditures.