Rock Form, which is worth at least £1 million, has been controversially removed from the shopping centre while a £30m revamp goes ahead. People now fear it will be sold off by owners Delancy and Royal Bank of Scotland.
More than 2,000 people have signed a petition asking for it to be returned and the council has written to Chancellor George Osbourne asking for help.
Now Sir Antony, whose most famous work is the Angel of the North in Gateshead, has backed the campaign to get Rock Form returned.
"It was made for this site and should be considered site-specific: it belongs to the building and the building is there to serve the citizens," he said.
"There is no doubt that, irrespective of the ownership of the building, the work should be replaced and continue to give joy to those who pass through the Mander Centre."
Rock Form had stood in the centre since it opened in 1968 but went missing earlier this year, sparking a campaign to get it returned.
A similar piece recently sold for £5m and there are fears that Delancey and RBS are looking to cash in by selling the artwork off.
Now an internal Delancey document has been leaked online in which the firm, to a question about whether the sculpture will be brought back after the Mander Centre is developed, states: "We are reviewing a number of public art installations for the redeveloped centre.
"We are also considering an artwork competition, which may help us to reach our decision"
The document has enraged supporters of campaign, with one saying it showed the 'contempt' the firm had for the people of Wolverhampton.
Delancey spokeswoman Olivia Gregory said: "We understand that no firm decision has been made, but believe that RBS are looking at options which will allow the sculpture to be enjoyed by the local community of Wolverhampton in the future.
"The art competition referred to in the draft Q&As (published by Richard Warren) was an idea which was considered back in May regarding other artwork for the centre, however due to the pending sale of the centre, this has not been progressed any further."
The row over the future of the sculpture, by Barbara Hepworth, has rumbled on for three months.
RBS said no decision has been made on the future of the sculpture.