Cologne chiefs accept they cannot keep hold of Timo Horn forever.
The young goalkeeper, 21, is tied to Cologne until 2019, having signed the deal before Christmas.
Horn's form has attracted interest from Arsenal and Liverpool in England, along with major Bundesliga clubs.
"Timo is one of the young guns who will eventually get their chance in the national team," said club vice-chairman Toni Schumacher.
"We are closely controlled by our financial abilities. So when a big club comes forward, with the right offer, we cannot say 'no'."
It's been revealed Horn's current deal carries a €9 million buyout clause, though given Cologne's precarious financial situation he could be sold be significantly less this summer.