This week the AFL and the Melbourne Cricket Ground are expected to sign an agreement giving interstate teams the chance to host preliminary finals.

In the past Ballarat has reaped a windfall from Adelaide and Port Adelaide supporters travelling to finals games at the MCG.

In a bid to attract spending the city was promoted as a "Crow-friendly zone" and a "port of call for Power fans".

This week's agreement could mean that Adelaide or Port Adelaide supporters will play in South Australia rather than travelling through Ballarat to Melbourne if they make it into the preliminary finals.

Ballarat mayor David Vendy said the new agreement could spell a loss of millions for Ballarat businesses this year.

"It would definitely have an impact on Ballarat if the supporters weren't passing through," he said.

"People from South Australia spend millions of dollars over a weekend when they stop here overnight or have dinner here on the weekend."

Cr Vendy said he would prefer if all games were played in Melbourne.

Alfred Motor Inn owner John Gleeson agreed that the hospitality industry in Ballarat would miss the business.

"Last year we were full on Friday and Saturday when Port Adelaide played in the grand final," Mr Gleeson said.

"September's typically a busy time of year because of the school holidays, South St and other events, but when an Adelaide team is playing in the finals that's an even bigger boost for Ballarat."

Harrowfield House owner Jim Hocking organised buses of supporters from Adelaide to travel to Melbourne for finals in recent years.

"In the past we've sent five coachloads of people staying in Ballarat to the MCG, and we weren't the only ones," Mr Hocking said.

"Most people would stay for two days, which means they were buying six meals, staying one night in a motel, bed and breakfast or tourist park and buying petrol.

"It's hard to quantify in dollars how much they would spend in Ballarat, but it's a lot," he said.