BILD reports Newcastle have approached Erras.
The 24-year-old's contract runs out in 2020 - and may be available for as little at £5 million.
He's been reported as saying: "My contract expires in 2020, of course leaving crosses your mind.
"I can confirm that clubs from the Premier League and the Bundesliga have already approached my advisor. But my first point of contact will always be the club."