TAMPA — Hillsborough County's top administrator on Wednesday laid down the terms and deadline for striking a deal to build the Tampa Bay Rays a new $900 million stadium in Ybor City.

And if the Rays don't agree to the county's terms within the next three months?

Then County Administrator Mike Merrill declared that there will be no ballpark in Ybor City — and no Major League Baseball team in Tampa.

"If we can't come up with term sheet by March of next year we're basically done anyway," Merrill told commissioners during Wednesday's meeting.

Merrill said the county's pitch to the Rays promises a stadium financing deal largely made up of private dollars — a potentially ground-breaking proposal for MLB stadiums that are typically built with public dollars. But if the Rays don't agree to the county's framework by Jan. 1, and if a binding agreement isn't struck by the end of the 2019 spring training season, then Merrill said it won't happen.

He also said he hadn't yet heard from Rays executives or principal owner Stu Sternberg about the county's offer, which he outlined in a memo last week.

The Rays declined to comment Wednesday to the Tampa Bay Times. County Commissioner Ken Hagan, who has taken the lead in negotiating a Hillsborough stadium deal, did not respond to a request for comment.

"We've got nothing else after this," Merrill said. "This is the best we can do."

The parties have about three months to work out a deal. A key player in the effort, Tampa Mayor Bob Buckhorn, also leaves office on May 1. So if an Ybor City ballpark near Adamo and Channelside Drives doesn't materialize before then, Merrill said, then it probably never will.

"The chance of a new mayor taking this on is very unlikely," Merrill said.

The county's proposal outlines two possible sources of private funding: Investors could put their cash into a federally-designated Opportunity Zone and landowners in and around the site could agree to tax themselves as part of a Community Development District.

The only significant public money would come from two of Tampa's Community Redevelopment Areas that would pay for infrastructure upgrades such as utility and road improvements.

The city would control zoning and land-use decisions as well as the CRA money, but county commissioners would be responsible for exempting the ballpark from property taxes, Merrill said, which could save the team and the stadium's private investors between $20 to $23 million a year.

"If property taxes have to be paid, cash flow doesn't work," Merrill said. "This is a deal that's never been done before on a stadium. We're laying off cost and risk to the private sector and in exchange for that, they need something to make the deal work."

Hagan, who commissioners gave the task of securing a new Hillsborough stadium site in 2014, was not at the meeting. He was in New York City on behalf of the Tampa Sports Authority for the announcement that Tampa will be awarded a franchise by the relaunched XFL professional football league.

In his absence, Commissioner Pat Kemp said the county should replace Hagan as its lead negotiator. She suggested it should be Merrill so that the Hillsborough County Commission can receive regular updates without violating the Sunshine Law, which prohibits commissioners from speaking privately to each other.

Hagan was also the subject of a 10News WTSP report that said he improperly coordinated with Darryl Shaw, the CEO of the BluePearl veterinary practice, who bought property within the footprint of the proposed stadium site. St. Petersburg Mayor Rick Kriseman criticized Hagan and asked that he be removed from Hillsborough's stadium effort. Hagan defended his role in the process and asked county staff to determine whether a defamation lawsuit can be filed against the TV station.

Commission chair Les Miller objected to Kemp's motion, saying Hagan wasn't able to defend himself and thought no commissioner, including Kemp, would want to be removed from a post while away on official business.

"That's not fair to any of us," Miller said.

Kemp agreed to withdraw her motion and bring it back at the commission's first meeting in January after being assured by Merrill that no substantive negotiations would take place in the last remaining weeks of 2018.

The Rays now face the task of hammering out an extension of their memorandum of understanding with St. Petersburg that would allow the team to negotiate in Hillsborough in 2019. Such an extension could cost the team millions of dollars and push back a first pitch at the Ybor City ballpark by a year to 2024.

Kriseman said he hasn't talked to the Rays about extending their agreement with the city, which St. Petersburg City Council first approved in 2016.

"There are some issues that need to be resolved if that were to occur, as my city needs some certainty regarding this matter," Kriseman said in a statement. "We tried to accomplish that by giving the team three years to look around.

"Both Hillsborough County and Tampa have had many more years to prepare for this, so it's unfortunate to see so much ninth inning scrambling."

Contact Charlie Frago at cfrago@tampabay.com. Follow @CharlieFrago.