The Manchester City player racially abused Newcastle United supporters during Saturday's game at St James' Park.
Northumbria Police confirmed they were investigating a complaint following Saturday's match.
It is alleged Serbia international defender Kolarov, 27, made comments to fans holding an Albanian flag.
Kolarov is understood to vehemently deny the allegation.
The player came on as a substitute in City's 3-1 win over Newcastle but was replaced 18 minutes from time.
Police have asked for anyone who heard or saw anything, or has any information, to contact them.
So if you saw anything ... errrrrr .... phone 999 and ask for Geordie Plod.
Source: Manchester City MAD
Source: FOOTYMAD
