A “shameful” image mocking the death of Cardiff City striker Emiliano Sala is being investigated by police.
Fans have condemned a photo – which reportedly shows a fake boarding pass – shared online in the run-up to the Bluebirds’ clash with bitter rivals Swansea on Sunday.
Sala, 28, died when the plane he was travelling in crashed in January.
South Wales Police said its probe was in relation to an offence under the Malicious Communications Act.
The force said it was working with both clubs to identify the source.
On Friday, Swansea issued a statement saying the “image is shameful and does not represent this football club or our supporters in any way”.
Swansea host Cardiff in the Championship game at midday on Sunday.
“We have a zero-tolerance policy towards any discriminatory, unacceptable or anti-social behaviour, and this will be enforced rigorously before, during and after Sunday’s South Wales derby,” said Swansea’s statement.
A police statement said: “We would remind people not to share the image as they may be committing an offence.”