Swansea have condemned a "disgraceful image" on social media mocking the death of Cardiff striker Emiliano Sala.
The club said the image "does not represent this football club or our supporters in any way" and confirmed they were working with South Wales Police, who will investigate.
Argentine Sala died in January aged 28 when the plane he was travelling in crashed in the English Channel.
Swansea host Cardiff in the Championship at midday on Sunday.
Before the first south Wales derby in five years, a Swansea statement added: "Any supporters displaying this type of material or behaving in an unacceptable manner will face criminal proceedings.
"The club will be strongly supporting South Wales Police in any public order or hate crime prosecutions surrounding these images and any related incidents during Sunday's fixture at the Liberty Stadium."