The Football Association is investigating a banner unfurled by Crystal Palace fans that depicted Nottingham Forest owner Evangelos Marinakis holding a gun to midfielder Morgan Gibbs-White's head.
Forest are hugely disappointed that supporters were permitted to bring the banner into Selhurst Park, according to well-placed sources.
Crystal Palace have been approached for comment by the BBC.
Palace and Forest played out a 1-1 draw at Selhurst Park on Sunday but the clash was overshadowed by the banner which, in addition to the portrayal of Marinakis pointing a gun towards Gibbs-White, read: "Mr Marinakis is not involved in blackmail, match-fixing, drug trafficking or corruption!