According to the Manchester Evening News, a Reds supporter sneaked in to an official post-game function to toast the winners, an event which needed accreditation, before confronting the former Anfield star.
Sterling was booed by the Merseyside faithful throughout the game, which Man City won in a penalty shoot-out with the scores locked at 1-1 after 120 minutes.
Following the trophy presentation and on-pitch antics, the City squad made their way to a Wembley lounge for a toast with sponsors.
Witnesses said, as he entered the function, Sterling was ‘grabbed’ by the fan, who then said ‘You F***ing Judas’.
But before the shaken 21-year-old could react, team-mate Kevin de Bruyne stepped in along with security personnel to break up the grapple.
The toast then continued, with Sterling posing for pictures and greeting fans before leaving with the rest of the squad for their flight back to Manchester.