Fortuna Dusseldorf are open to holding onto Manchester City goalkeeper Zak Steffen.
The American goalkeeper is already impressing in the first weeks of his season-long loan.
Fortuna Dusseldorf chief Thomas Rottgermann told dpa: "Unfortunately, we could not agree to a purchase option with Manchester.
"That does not necessarily mean that we lose Zack Steffen at the end of the season.
"You should not underestimate our tenacity."
