Sky sources understand Eintracht Frankfurt have told Sunderland that Bastian Oczipka is not for sale after they made an enquiry for the left-back.
Sunderland asked about the availability of the 24-year-old, who is understood to be open to a move to the Premier League.
Oczipka still has two years left on his contract after signing from Bayer Leverkusen in 2012.
A source in Germany told Sky Tyne and Wear: "There was a direct phone call between both clubs, Sunderland made an enquiry but Frankfurt are not open to sell."
Germany head coach Joachim Löw has been impressed by Oczipka and is considering selecting him for the national side. A move to the Premier League may help his chances of playing in the World Cup next year.
The source said: "The Premier League is always interesting. Sunderland would be a reasonable step for him."
Sunderland are still searching for a left-back after their move for Benjamin Mendy was hijacked by Marseille and Lucas Orban continues to delay making a decision on his future with Spanish side Villarreal also credited with an interest in him.