The artwork which appeared in the city in October 2020 has been removed and sold.
Gallery owner John Brandler told the BBC he paid a “six-figure sum” for the piece, and wanted to help preserve it, as well as put it on display.
Mr Brandler said the workers were part of a “very specialised company” which had removed Banksy art before.
He claimed he had saved the Nottingham artwork “in time” before damp could cause damage under the plastic cover put on by Nottingham City Council.
“If you put Perspex over a picture the moisture gets into the brick wall and can’t escape – the wall needs to breathe,” he said.
Mr Brandler said he planned to feature the piece in a street exhibition later this year at the Moyse’s Hall Museum in Bury St Edmunds, Suffolk.
Nottingham City Council said:
‘The City Council wasn’t aware of these plans [ to remove the artwork ] and of course it’s regrettable that it has not been kept in Nottingham for local people to continue to enjoy.
‘We were pleased that while the Banksy was in place, local residents were fortunate to see and enjoy it.
‘We explored options to secure the artwork for the city with the Nottingham Project, who contacted representatives for Banksy.
‘They asked for the artwork to remain in situ and the artist’s wishes were respected.
‘Ultimately, once those options were exhausted, it was for the property owner to decide what to do with it.’