The Leeds defender has joined Eintracht Frankfurt on a season-long loan deal in the summer transfer window.
Koch was keen to leave Leeds following their relegation from the Premier League and found a taker in Eintracht Frankfurt this summer.
Eintracht Frankfurt have also agreed to pay a loan fee of €500,000 to Leeds as part of the deal but the defender could stay on beyond the end of next season.
According to German magazine Kicker (via Fussball Transfers), Eintracht Frankfurt already have a deal in place with Koch for him to stay beyond the end of his loan stint.
The German club’s announcement only mentioned a season-long loan agreement for the defender.
But it has been claimed that the defender has a verbal agreement in place with Eintracht Frankfurt for a long-term contract.
With Koch not having signed a new contract at Leeds, he is out of contract next summer and has effectively departed Elland Road for good.