Sal Paolantonio shares what he learned in his conversation with Roger Goodell about the Raiders' future in Las Vegas. (1:52)

Just days before NFL owners are set to vote on a potential Raiders move to Las Vegas, commissioner Roger Goodell wrote to Oakland Mayor Libby Schaaf and said, in part, that he believes the city has yet to find "a viable solution" to keeping the team there.

The letter, obtained by ESPN, was sent Friday, the same day the city of Oakland and its partners submitted a revised financing plan for a $1.3 billion mixed-use stadium project on the same site where the team currently plays.

Goodell said the league office reviewed the proposal and still believes there are significant problems with it.

"The material that we reviewed earlier today ... confirms that key issues that we have identified as threshold considerations are simply not resolvable in a reasonable time," the commissioner said in the letter, "and in that respect, the information sent today does not present a proposal that is clear and specific, actionable in a reasonable time frame and free of major contingencies."

It's a seemingly negative development for Oakland, with NFL owners expected to vote as early as Monday on owner Mark Davis' application to move his franchise from the city to Las Vegas, where city, county and state officials have pledged $750 million in public funding toward a new stadium there. Davis needs at least 24 "yes" votes from the 32 owners to leave Oakland.

Roger Goodell joined players to see how they impact criminal justice reform. Allison Joyce/Getty Images

In an interview with ESPN's Jim Trotter on Friday, Schaaf acknowledged that time and momentum are working against her city. But she said she believes Oakland's latest financing plan -- submitted on behalf of the city, Alameda County, the Oakland City Pro Football Group and Fortress Investment Group -- adequately addresses the concerns expressed by the league in recent months, most notably the substantial presence of Fortress, a private equity firm.

The league did not like that Fortress was acting as a vendor/guarantor of things such as personal seat licenses, sponsorships and suites, so Fortress now has agreed to commit $650 million in a traditional loan, if the league and Raiders prefer. As for the remainder of the financing in the latest proposal:

• The city would make a $200 million commitment in infrastructure improvements, with Fortress advancing it $150 million through conveyance of up to 130 acres on the site where the stadium would be part of a mixed-use project. The $150 million would be repaid to Fortress on the back end through tax increments.

• The Raiders and the NFL would contribute $500 million.

• Under the city's plan, a new home for the Raiders would be built on a 55-acre parcel on the southern edge of where their current stadium sits. According to the plan, Major League Baseball's Oakland Athletics could continue to play in Oakland-Alameda County Coliseum while a football-only venue is constructed.

While Oakland city officials don't believe the presence of two pro franchises is an issue -- pointing out that MLB and NFL teams share similar setups in Seattle, Baltimore and Arlington, Texas -- Goodell reiterated the league's concern with the A's situation, as well as other worries, in the letter.

"We have been prepared for nearly two years to work on finding a solution based on access to land at a certain cost, without constraints on the location of the stadium or timing of construction, and clarity on overall development," the commissioner told Schaaf. "However, at this date, there remains no certainty regarding how the site will be fully developed, or the specific and contractually defined nature of the participation by Fortress or other parties. In addition, the long-term nature of the commitment to the A's remains a significant complication, and the resolution of that issue remains unknown. Other significant uncertainties, which we have previously identified, remain unaddressed.

"Despite all of these efforts, ours and yours, we have not yet identified a viable solution. It is disappointing to me and our clubs to have come to that conclusion."

The Raiders have called Oakland home for 45 of their 58 seasons, including each of the past 22.