Celtic manager Neil Lennon was reportedly spat upon while watching Aberdeen's League Cup semi-final against St Johnstone.
Lennon's agent, Martin Reilly, told BBC Scotland that Lennon had coins thrown at him and was spat upon during the game at Tynecastle.
It is understood Lennon walked out of the stadium shortly after Adam Rooney scored the third goal in the 62nd minute of Aberdeen's 4-0 victory.
Lennon was sitting in the main stand at Tynecastle, yards above the technical area where he was attacked by a Hearts fan during a game in 2011. The stand was housing Aberdeen fans on Saturday.
Celtic hit out at the behaviour of some supporters in the stand.
A club spokesperson told Press Association Sport: "Clearly it is totally unacceptable for the Celtic manager to be treated in this way.
"Neil has complimented the way in which the situation was handled by stewarding staff at Tynecastle.
"We have an excellent relationship with Aberdeen Football Club and we are sure they will look into this matter."
Aberdeen, who reached their first cup final since 2000, pleaded for supporters to report those responsible.
In a statement on their official website, a Dons spokesperson said: "The support we enjoyed at Tynecastle was absolutely fantastic and helped to create an incredible atmosphere that the manager and players acknowledged played a major part in what was wonderful day and occasion for Aberdeen Football Club.
"However, it would appear that a tiny minority within the main stand behaved in a manner that is completely unacceptable and has absolutely no place in football and we would urge anyone who has any information as to the identity of those responsible to get in touch with the club in order that appropriate action can be taken."
Quoted on the BBC Scotland.website, Lennon's agent, Reilly, said: "I'm absolutely raging about the treatment of Neil, about the stewarding and the fans' behaviour. It's scandalous that Neil is treated like this."