An anonymous artist painted gates of the former Muhammad Ali Centre in Birmingham, opened by the former boxer in 1983.
The site is council-owned but managed by community group the Kajans Womens Enterprise in Aston.
The artwork was reported missing on 17 June, said West Midlands Police.
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The painting, that appeared after Muhammad Ali's death, featured the three time world champion with a butterfly, echoing his renowned catchphrase: "float like a butterfly, sting like a bee."
Hermin Macintosh from Kajan Womens Enterprise said: "The creativity of the artist was fantastic so we wanted to save it.
"Ali was a world-class fellow and his contribution went across all cultures and communities, so the mural was for everyone and welcomed by everyone."
The centre had been boarded up since 1998 and Kajans are sifting through ideas from the public about how it should be developed.
"The artist could have gone anywhere but they specifically chose this site because Ali opened it," said Ms Macintosh.
"If there is an opportunity for it to be returned it would be welcomed by everyone."
A Banksy-style mural of Muhammad Ali that appeared after his death has been stolen from a site that the  boxing legend once opened.