The £25,000 sculpture was covered in pink paint between Saturday night and Sunday morning.
The words “Gotta love art” and “RIP” were also daubed on its marble plinth. Police are appealing for witnesses and are keeping an open mind about the vandals’ motives, but it does not appear to be connected to football rivalry.
Blackbird Leys Neighbourhood Sergeant Rob Axe, pictured above left with Pc Kirk Rogers and Pc Sandra Timms, said officers were alerted to the damage at about 8am on Sunday as they arrived to police the stadium's car boot sale.
Sgt Axe said he believed it was the first time the statue had been vandalised since it was put up in February 2008.
He said CCTV footage revealed two figures walking past the stadium on Saturday night, but evidence is still being gathered.
United chairman Kelvin Thomas said: “We’ll do some work this week to see if we can get it back to its former glory, but it’s disappointing someone feels the need to express themselves in this way.”
Anyone with information should call Sgt Axe on 08458 505505 or call Crimestoppers anonymously on 0800 555111.