Cardiff Blues are investigating an incident which saw a spectator throw a drink towards assistant referee George Clancy during their 20-19 Pro 14 defeat by Glasgow at Cardiff Arms Park.
The Welsh region say the man was ejected from the ground and that "appropriate action" will follow.
A statement said: "The club are now conducting a thorough investigation. Once investigations are concluded the appropriate action will be taken."
South Wales Constabulary say they have not received a complaint and are not investigating.