An image purporting to show the moment Robert Hart was fatally struck at the Parklife Weekender festival relates to a seperate incident and does not show the 26-year-old being assaulted.
An eye witness posted a photo of an alleged attack onto social media, sparking rumours it showed the culprit who killed Hart.
But Greater Manchester Police has moved to quash those claims, saying the photo relates to a seperate attack and not the one that killed Hart.
The call centre employee was knocked unconscious as US rapper Snoop Dog was about to take to the stage at Heaton Park, in Manchester, on June 7.
Despite being given CPR by an off-duty midwife at the scene, Hart, who was from Macclesfield, died four days later at North Manchester General hospital.
The attack happened after his girlfriend had been repeatedly hit with an inflatable toy in the 18-000-person crowd.
Greater Manchester Police said on Facebook: "We are aware of an image circulating on social media that has been wrongly identified as a photograph of the assault on #RobertHart at #Parklife2014. It appears to show an attack while people stand by and watch.
"We would like to make it clear that this image is unrelated and there is no connection to the attack on Robert. Although the image is unrelated, we would like to thank you for your help in trying to identify the person responsible for the assault on Robert."