Raheem Sterling was allegedly kicked and racially abused as he arrived to Manchester City's match on Saturday against Tottenham Hotspur.
Sterling went on to score two goals in the match.
A GMP spokesperson said: “On Sunday 17 December 2017, police were made aware that a 23-year-old man had been subject to a racially aggravated assault on Clayton Lane on Saturday 16 December.
“While an official report has not yet been made, enquiries will be carried out and officers are treating it as a hate crime.
“Hate crime will not be tolerated in Greater Manchester and can be reported via the True Vision website at report-it.org.uk
“Anyone with information about the incident should contact police on 101 or the independent charity Crimestoppers, anonymously, on 0800 555 111.”