Prince’s sister, Tyka Nelson, made the announcement in July: A Prince tribute concert Oct. 13 at the new U.S. Bank ­Stadium in Minneapolis.

But a month before the much-ballyhooed show, the stadium doesn’t have a signed contract and the Prince estate has not announced any acts or ticket information. To sell more than 40,000 seats for a concert in a football stadium usually requires months of promotion.

“There is not a contract yet. Discussions continue to finalize concert details,” Michele Kelm-Helgen, chairwoman of the Minnesota Sports Facilities Authority that oversees the Vikings stadium, said via e-mail on Tuesday.

Prince fans from around the world have been expressing their frustrations because they booked plane and hotel reservations planning to attend the concert, but they’ve been left in the dark about details.

“It’s frustrating that I got this far into it, and there’s a vacuum of information,” said Ingrid Ostrom of Greensboro, N.C. She bought airline and Paisley Park tour tickets, made hotel reservations, and planned to take four days of unpaid leave from work and pull her 14-year-old son out of school to visit Minnesota. “There are other Prince tributes like Sheila E. in Cleveland, but Minneapolis is the important place to be. That has meaning.”

L. Londell McMillan, one of two music advisers to the Prince estate, is ostensibly in charge of the U.S. Bank Stadium concert. He did not respond to e-mails or texts from the Star Tribune asking about the concert. But Sunday on Twitter, he wrote: “Big Week Ahead! #KeepTheFaith.”

This came after a previous promise in August of ticket information being announced after Labor Day. But there has been no word — just vague postings by McMillan on Twitter.

Since Prince was found dead of an accidental painkiller overdose on April 21, there has been much confusion about his heirs and estate. Working with Bremer Bank as estate manager, Prince’s six siblings have turned to McMillan and veteran music-business executive Charles Koppelman, who has recently been involved with the careers of Adam Levine and Nicki Minaj, as paid consultants on how to exploit the assets of Prince’s estate, which has been valued from $100 million to $300 million.

Among the projects is opening Paisley Park, Prince’s longtime studio complex in Chanhassen, for tours at $38.50 a ticket ($100 for VIP), starting Oct. 6. .

Sources have indicated that the producer for the stadium show has been changing. First, Jobu Productions, a little-known East Coast company that was relying on hedge-fund investors, was involved.

Then apparently Live Nation, the world’s largest promoter, kicked the tires and eventually passed.

Influential talent manager Irving Azoff, who is regarded as one of the most powerful figures in the music business, has been brought in to help, talking about delivering such acts as Stevie Wonder, John Mayer, Chaka Khan and Christina Aguilera, who is one of his clients.

Azoff has a long history of working with Minneapolis promoter Randy Levy, who was enlisted late last week to oversee the production aspects. “There are some t’s to cross and i’s to dot with the stadium,” Levy said Tuesday, “but it’s progressing, and we’ll put together a terrific show.”

Other Prince-related acts including Morris Day and the Time and the Revolution are rumored to be participating. A spokesman for the Revolution, Prince’s “Purple Rain” era band, said the group is still talking to concert organizers.

Mint Condition, a veteran Twin Cities R&B band best known for the 1991 hit “Breakin’ My Heart (Pretty Brown Eyes),” is the only act that lists Oct. 13 at U.S. Bank Stadium on its itinerary.

At least, the only act so far.