FIFA has confirmed they are investigating a complaint filed by Loris Karius against Besiktas.
Liverpool goalkeeper Karius is coming towards the end of a two-year loan spell at the Turkish club and was expected to join them on a permanent basis at the conclusion of the deal
Last month, there were reports the 26-year-old had filed a complaint against the Istanbul club relating to alleged unpaid wages.
A FIFA spokesperson said: "We can confirm that we have received a claim from the player Loris Karius against the club Besiktas.
"The matter is currently being investigated and consequently we cannot provide any further comment."
Sky Sports News has contacted Besiktas for a response.