The Asian Football Confederation (AFC) is set to investigate after fans of Chinese club Guangzhou Evergrande displayed a banner reading "Annihilate British dogs" during their 6-0 Asian Champions League victory over Hong Kong champions Eastern.
The banner at Eastern's Mong Kok Stadium also described Hong Kong's independence movement as "poison."
Hong Kong is a former British colony that returned to Chinese rule in 1997. The territory retains a separate economic, legal and political system from the communist-governed Chinese mainland until 2047 under the "one country, two systems" law, but there have been bitter political divisions between pro-democracy activists and Beijing loyalists in recent years.
The AFC's safety and security regulations say political messages are "strictly prohibited before, during and after" games and that "the Match Organiser, together with the Security Officer and the chief police officer or Stadium security officer, shall prevent any provocative action being taken by spectators inside or in the immediate vicinity of the Stadium," including "provocative banners."
Hong Kong's South China Morning Post newspaper quoted a Hong Kong FA source as saying: "We informed the match commissioner of the banner content, and he has put it in his report to the AFC.
"This banner is not allowed as they never applied to display it, but we don't know how they got away with the bag search. We will have to investigate."
A spokesperson for the AFC told Reuters that it is "waiting for the match commissioner's report and then the AFC will make a full assessment of the facts."
- Football in HK (@offsideHK) April 25, 2017
Eastern executive director Peter Leung Shou-chi, meanwhile, has told the South China Morning Post that one of the home side's coaches was "slammed in the face by people from Evergrande" in the tunnel at half-time, when the Chinese side led 2-0.
The Hong Kong-based newspaper reported that there was "pushing and shoving involving players and coaching staff from both sides" during the incident.
Leung confirmed Eastern would submit a report to the AFC and said: "We were greatly concerned about the matches against Guangzhou after the draw was made and put in place a lot measures, but still some other things were out of our control.
"We are very disappointed to see things like this happen as it brings bad reputation to the game.
"We don't know what kind of sanctions the governing body will apply after reading the report. We do what the rules require us to do."
Information from The Associated Press was used in this report.