TAMPA — The Rays' proposed Ybor City ballpark could spur the construction of 4 million square feet of surrounding development, according to a study commissioned by the team.

The revenue generated by that development is part of the county's plan to build the estimated $900 million stadium. By comparison, downtown Tampa has about 6.1 million square feet of downtown office space. The new Water Street Tampa project is expected to create 9 million square feet of office, retail and residential space.

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The existence of the study and that key figure in the stadium financing deal Hillsborough County offered to the team was cited in a letter sent this week on behalf of local leaders to MLB commissioner Rob Manfred and Rays owner Stu Sternberg.

County officials hope Manfred will urge the Rays to accept the deal.

Hillsborough County Administrator Mike Merrill said the decision to involve Manfred makes sense. Merrill has set a deadline of the end of the 2019 spring training season to get a deal done — otherwise he has warned baseball may not come to Tampa.

"The baseball commissioner has influence on how a deal such as this gets done and chooses whether or not to become involved," Merrrill said. "As I understand it, the baseball commissioner has to approve deals anyway."

The Rays have not responded to the county's proposal. The team has also not responded to requests for comment from the Tampa Bay Times.

The letter was drafted by Irwin Raij, an attorney working on behalf of the Tampa Sports Authority who specializes in stadium deals. He wrote that the proposal "represents what leadership believes the community could support."

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Although the ballpark would be publicly owned, the letter says the county expects the Rays to be responsible for overseeing constructions. The team would also pay $3 million in annual rent payments that would be set aside to pay for stadium maintenance and future upgrades. Those payments would also increase over time.

The deal allows the team to build a 50,000 square foot sports medicine facility near the ballpark that could be used by the team and the public. The Rays would also receive all revenue generated by the stadium, such as ticket and concessions sales, except when it's being used to host community events.

Development around the ballpark would be critical in helping pay the estimated $892 million price tag. A portion of the county's $475 million share of the cost is expected to come from property taxes collected in two of Tampa's Community Redevelopment Areas. New development in those areas would increase property tax collections. By law, those taxes can only be spent within the district boundary.

Also, a number of landowners in and around the site have indicated a willingness to tax themselves as part of a Community Development District in the expectation that their properties would become more valuable.

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Were that 4 million square feet of new construction to materialize, it would mean new development would spread well beyond the ballpark, located where Ybor City meets the Channel District..

The study was conducted by RCLCO, a real estate firm headquartered in Washington D.C., and has not been released by the Rays.

Most of the money for the ballpark is expected to come from private investors putting their cash into a federally-designated Opportunity Zone the ballpark would lie within. A new law intended to spur redevelopment of low-income areas allows investors to avoid paying taxes on profits earned elsewhere for up to 10 years.

Merrill acknowledged that officials have not ruled out using Community Redevelopment Area property taxes to make up any shortfall in the county's share of the ballpark.

"The districts were established long ago before there was even an idea the stadium would go there and the dollars have to stay in those CRA districts anyway," he said.

Spending of those funds would have to be approved by Tampa City Council, in addition to any zoning and land-use decisions.

Tampa City Council member Charlie Miranda said at Thursday's meeting that he is tired of being left in the dark regarding ballpark negotiations. At his request, council members agreed to discuss next week whether they should hold public hearings on the Rays deal.

Mayor Bob Buckhorn said it's time for the Rays to respond to the county's offer:

"There have been no commitments made by the City other than to our best efforts to work to see if this deal is attainable and if not, to be prepared to walk away and wish them well in St. Petersburg"

Staff writer Charlie Frago contributed to this report. Contact Christopher O'Donnell at codonnell@tampabay.com or (813) 226-3446. Follow @codonnell_times.