The blaze at Wythenshawe Hall on Tuesday ripped through the roof and upper floor of the Tudor building and was tackled by 50 firefighters.
A campaign to save the timber-framed hall built in 1540 has now been launched by local Labour MP Mike Kane.
Greater Manchester Police (GMP) say they "believe" the fire was arson, but are "investigating all possibilities".
Greater Manchester Fire and Rescue search dogs were taken into the building on Wednesday to try and identify how and where the fire started.
Insp Luke Breakspear, of GMP, said: "We have reason to believe the fire was arson. We are doing all we can to get to the bottom of what happened.
"We are still appealing for anyone with any information to come forward."
The running of the building, which is owned by Manchester City Council, was recently taken over by the Friends of Wythenshawe Hall.
Members of the group applauded firefighters after they tackled the blaze.
The group's vice chairman Paul Selby said: "I got the call in the morning to say the hall was on fire. It was one of the worst calls I've had.
"Just below the roof is the Withdrawing Room - one of the most spectacular rooms in the building. It was all set up with period costumes."
Mr Kane, MP for Wythenshawe and Sale East, has vowed to save the hall which was home to the Tatton family for hundreds of years.
He told BBC Radio Manchester: "We are already setting up meetings with the council, the friends group and councillors to form a plan as to how we can secure the necessary funding to restore the hall.
"I have brought the issue to the attention of the Department for Culture, Media and Sport.
"The community in Wythenshawe will be right behind the campaign."
The fire that partially destroyed a 16th Century hall in Manchester was arson, police have said.