He was found at the bottom of a flight of stairs in the Bucksburn area of the city, and has been taken to the Aberdeen Royal Infirmanry.
Cooper played for Aston Villa, Reading, Rangers and others as well as Aberdeen as part of a successful career. He won two league titles with Aberdeen.
"Police inquiries were ongoing throughout the night to establish the full circumstances, however the incident does not appear to be suspicious," David Howieson, of Police Scotland North East, said.
"I would like to thank the local community for their patience whilst we have dealt with the incident."