Crystal Palace have joined the clubs to have enquired about Schalke defender Ozan Kabak.
Manchester United, Leicester City and RB Leipzig are all monitoring developments with the Turk, who is available for around £25million.
Palace are looking to offload centre halves James Tomkins and Mamadou Sakho who are coming towards the end of their contracts and are evaluating targets across Europe.
Palace also have Scott Dann, now 33, and Gary Cahill at 35 and want to reduce the average age of their playing squad.
The Eagles have only kept one clean sheet this season - the fewest in the Premier League - on the opening day against Southampton.