Fulham are investigating an allegation that defender Cyrus Christie's sister was hit and racially abused during the Cottagers' 1-0 defeat at Barnsley.
The Republic of Ireland international alleged the incident took place at Oakwell on Saturday, the opening day of the Sky Bet Championship season.
Christie wrote on Twitter after the game: "To the Fulham fan that decided to hit my sister at the game today and his wife who justified his action with racist remarks I hope you're proud of yourself and feel like a big man.
"You'll get what's coming to you. Regardless how you felt about the result your actions are shameful."
Fulham announced in a statement the club will take "the strongest possible action".
"Fulham Football Club is investigating an incident which took place in the away end at the Barnsley v Fulham fixture this afternoon," a statement read.
"Should the perpetrators be identified, the club will be taking the strongest possible action."
