Local detectives, the Arson Squad and CFA investigators took the 71-year-old Flowerdale man into custody on Wednesday then released him pending further inquiries.
The fire is believed to have started in the Spring Valley Road area on Tuesday afternoon before spreading to nearby bushland.
The blaze has grown to more than 780 hectares, with the northeasterly flank of the fire the most active on Wednesday evening.
An emergency warning was issued for Flowerdale residents but it was downgraded on Wednesday morning.
People in Flowerdale, Dairy Creek, Homewood, Kerrisdale and Strath Creek are urged to monitor conditions and be prepared to act.
More than 100 firefighters and 10 water-bombing aircraft have been battling the grassfire across steep, inaccessible terrain.
No homes have been lost but one property was partially damaged in the blaze, Emergency Management Commissioner Andrew Crisp said.
"We are literally throwing everything at this particular fire but there's still a lot of work to be done," he told reporters on Wednesday.
Smoke is visible across the area. An incident control centre has been set up at Alexandra and a relief centre has opened at the Yea Recreation Reserve.
A community meeting was due to be held at the reserve at 6pm on Wednesday.
Mr Crisp said Flowerdale residents might be feeling on edge as the town was one of those devastated by the Black Saturday fires.
Some 173 people lost their lives in the 2009 bushfires, which tore through more than 450,000 hectares of land.
"I'm sure people in the Flowerdale area are triggered, a number of them, by what they're seeing, what they're hearing, what they're smelling at the moment," Mr Crisp said.
"However, we've also received feedback from local residents about how great it is to see everything working so well."
Crews hope to contain the blaze before Friday, when temperatures will nudge 40C and winds will pick up ahead of a Saturday cool change.
"The next couple of days will be challenging for firefighters," CFA chief officer Jason Heffernan told reporters.
The Wimmera region in the state's northwest, on the other side of Victoria from Flowerdale, is expected to have an extreme fire danger rating on Friday as other parts of the state remain on high alert.
This year's fire season could continue for some weeks after the October floods created excess vegetation.
"I do expect March to still be reasonably warm and dry so communities can't be complacent," Mr Heffernan said.
"That fuel is out there and we need to make sure that you've got your bushfire survival plan."
Victorians are also being reminded to extinguish their campfires when they leave an area, especially as the temperatures rise.
"Over 10 per cent of bushfires are caused by unattended campfires," Forest Fire Management chief Chris Hardman told reporters.
"If it's not cool to touch with your hand, it's not cool to leave."
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