According to the Manchester Evening News' Stuart Brennan, a Liverpool supporter "yanked" the 21-year-old and called him a "f--king Judas" as Sterling entered an official post-match celebration in one of Wembley's lounges.
Sterling was inevitably booed by Liverpool fans throughout the match following his summer move from Anfield to the Etihad, but City were eventual winners on the night, taking the shootout 3-1 after the contest finished 1-1.
Brennan added that City winger Kevin De Bruyne and a security guard stepped in to prevent the altercation from going any further.
Sterling's departure from the Merseyside club—where he had advanced through the youth ranks—was messy.
He initially turned down the offer for a new contract with Liverpool before asking to leave the club and finally sealing a deal with Manchester City worth up to £49 million, per BBC Sport.
Sunday was the first time Sterling had faced Liverpool away from the home comforts of the Etihad Stadium, and he received a fair amount of abuse during the match from the 30,000 Reds fans.
The Englishman also did not have the best game after missing a couple of chances to seal the triumph in normal time, per the Telegraph's Paul Hayward:
Indeed, Bleacher Report's Dean Jones believes Sterling was "let off the hook" by Willy Caballero's heroics in the penalty shootout:
Europe vs. South America—Who Would Win? We Simmed on FIFA17
Inside Transfer Deadline Day: Access All Areas at Sheffield United
FIFA Sim: Bundesliga All-Stars vs. Serie a All-Stars
Meet 'Billy the Wonder Kid': the 7-Year-Old Football Phenomenon
Juventus vs. Real Madrid: Champions League Final Goes Space Invaders
Gianluigi Buffon Is an All-Time Great: Will He Finally Win the Champions League?
Duong Ly Picks Football's Biggest Results: Who Wins the Champions League Final?
Can Real Madrid Unlock Juventus' Defense in UEFA Champions League Final?
FC Copenhagen Fans Throw Beach Toys on Pitch During Final Match of Season
Goodbye to Tottenham Hotspur's Famous Old Stadium—White Hart Lane
Blue Is the Colour—B/R Animation Celebrates Chelsea's Title
Lyngby Goalkeeper Makes Incredible Goalkeeping Blunder
We Asked Fans in Egypt: Who Is Your Champions League Legend?
Here Is What Happened When the Champions League Trophy Visited Egypt
6-Year-Old Prodigy Ariana Dos Santos Has Has Met Her Barcelona Heroes
Jamaican Fans Tell B/R Their UEFA Champions League Memories
Arsene Wenger Carries on Regardless as Arsenal Stars Cause Chaos in Background
N'golo Kante Will Win the PFA Players' Player of the Year Award
Dmytro Hrechyshkin Scores Fine Free-Kick for Vorskla—but Did He Mean It?
However, there is little excuse for his facing a physical confrontation from a Liverpool fan, and it is not known how the supporter in question was able to breach security and "get to an area where accreditation was needed," per Brennan.
In a quirk of the fixture list, City and Liverpool will face off again in the Premier League on Wednesday, and Sterling will not be expecting a warm welcome at Anfield.