HIBS yobs launched a glass bottle at Rangers star Borna Barisic as he lay injured on the pitch.
The Light Blues defender was targeted after he was brought down in a shocking challenge by Ryan Porteous, who was subsequently sent off.
That provoked angry scenes on the pitch as Barisic's team-mates surrounded the Hibs star as he made his way off the field.
While in the dugout, both sets of coaches angrily confronted each other over the incident, resulting in Gers coach Tom Culshaw and Easter Road No2 John Potter being shown red cards.
Hibs boss Jack Ross also had to be held back as he spoke to Rangers No2 Gary McAllister after the clash.
But as Barisic was still receiving treatment on the opposite side of the pitch, a bottle appeared to be thrown at him from the Hibs end.
Coffee cups could also be seen lying nearby, although they were there at the time of the foul itself.
Police quickly moved in with one officer then being spotted holding the empty bottle in his hand.
Speaking to BT Sport after the game, Rangers boss Steven Gerrard said: "I've spoken about that too many times now but that's Hibs' problem.
"That's for Jack Ross to deal with. If it was Rangers fans, I'd be extremely disappointed."
BBC reporter Brian McLaughlin told Sportsound that Hibs have vowed to find the person responsible.
He said: "I've just spoken to a Hibs spokesperson here and he's told me that the club have installed new CCTV cameras in the summer which allows them to identify every single seat at Easter Road.
"They will be reviewing the footage to try and identify those responsible for throwing items.
"I believe one of the items was a glass bottle that was thrown on to the side of the pitch as well.
"They will be reviewing the footage, they will identify them and try and find out exactly who they are."
SunSport have contacted Hibs for comment.
Rangers ultimately won the encounter 3-0 thanks to two early goals from Ryan Kent and Joe Aribo, and a second-half effort from Jermain Defoe.
Their victory moves them to within two points of league leaders Celtic, although Gerrard's men still have a game in hand.