The French defender’s contract will expire at the end of the season and Dortmund are in negotiations over a new deal to secure his future.
He is of interest to Premier League pair Manchester United and West Ham, who are considering taking him to England.
But Dortmund have been insisting that they want to hold on to the player and are pushing him to sign a new deal.
However, according to German magazine Kicker, doubts over his fitness are forcing the Bundesliga giants to have a rethink.
He has featured just nine times in the Bundesliga this season and suffered a fresh injury setback at the weekend.
Zagadou is currently out injured and Dortmund are feeling increasingly anxious about offering him a new deal.
The Bundesliga giants are having doubts over whether they can rely on him being fit for a full season.
The Frenchman has suffered numerous injuries since he joined Dortmund in 2017 and has made 86 appearances over the last four-and-a-half years.
