Nottinghamshire County Cricket Club is likely to receive the money from the city and county councils, along with Rushcliffe Borough Council.
Alan Rhodes, leader of the county council, said the money would be raised from a low-interest loan, which would be repaid by the club at a higher rate.
England beat Australia at Trent Bridge in August to regain the Ashes.
The city and borough councils have both already agreed to lend £2.7m each with County Hall due to make a decision on a similar figure at a meeting in October.
Two years ago the then Conservative-led County Hall came under fire for giving the club £900,000 towards a scoreboard.
At the time, Labour councillor Mr Rhodes described it as "insensitive" to be giving money while making cuts to services.
Since then, Mr Rhodes has become leader of the council but said this time it was different.
"We are providing that loan via our own lendings," he said.
"We are able to borrow money at a very low rate from the banks and we are able therefore to help Nottinghamshire County Cricket Club to be able to upgrade their facilities and they will pay that loan back with interest."
He added that the council could not take out similar loans to pay for ongoing costs such as care homes.
City council deputy leader Graham Chapman said the authority would get a higher rate of interest back on the loan than the current bank rate.
"We are going to get some money, they're going to save some money and we're going to get some very nice stands out of it," he said.
Nottinghamshire County Cricket Club would not comment before the final loan is agreed but it is understood the money would be used to revamp a stand and some facilities.
Work could start this winter.

The deal calls for an immediate truce and the formation of a transitional government ahead of the drafting of a new constitution and new elections.
The conflict in the world's newest state has left thousands dead and more than one million homeless.
A ceasefire agreed in January collapsed within days, with both sides accusing each other of restarting the fighting.
US Secretary of State John Kerry said Friday's agreement "could mark a breakthrough for the future of South Sudan".
"The hard journey on a long road begins now and the work must continue," added Mr Kerry, who played an instrumental role in bringing together the two sides.
The UN has accused both the South Sudanese government and the rebels of crimes against humanity, including mass killings and gang-rape.
The rivals signed the deal in the Ethiopian capital, Addis Ababa late on Friday, after their first face-to-face meeting since the hostilities began.
The BBC's Emmanuel Igunza in Addis Ababa says the agreement calls for a cessation of hostilities within 24 hours of the signing. A permanent ceasefire will then be worked on.
Mr Kiir and Mr Machar are to issue immediate orders for troops to end combat and to allow in humanitarian aid.
It was not immediately clear who would form the transitional administration.
The deal was also signed by Ethiopian Prime Minister Hailemariam Desalegn, who hosted the talks.
Alastair Leithead reports on rape and murder in Bentiu
Leading mediator Seyoum Mesfin, from the regional Igad bloc, congratulated Mr Kiir and Mr Machar for "ending the war".
However, African Union official Smail Chergui warned that "given the current crisis, the restoration of peace in South Sudan will not be easy".
A UN report released on Thursday said that "widespread and systematic" atrocities had been carried out by both sides in homes, hospitals, mosques, churches and UN compounds.
It called for those responsible to be held accountable.
An estimated five million people are in need of aid, the UN says.
The violence began when President Kiir accused his sacked deputy Mr Machar of plotting a coup.
Mr Machar denied the allegation, but then marshalled a rebel army to fight the government.
The battle assumed ethnic overtones, with Mr Machar relying heavily on fighters from his Nuer ethnic group and Mr Kiir from his Dinka community.
The UN has about 8,500 peacekeepers in South Sudan. However, they have struggled to contain the conflict.
South Sudan gained independence in 2011, breaking away from Sudan after decades of conflict between rebels and the Khartoum government.
It remains one of the world's poorest countries.
Trent Bridge cricket ground is set for a £8.1m revamp thanks to loans from three councils.
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South Sudan's President Salva Kiir and rebel leader Riek Machar have agreed a peace deal after a five-month conflict.