Borussia Monchengladbach chief Max Eberl admits Matthias Ginter and Denis Zakaria could be sold in January.
Zakaria is being linked with Liverpool and Manchester City, while Ginter is being watched Arsenal and Chelsea.
Eberl said, "In general, everyone has less. And the players have to choose: do I play poker and leave on a free transfer or not? There are so many risks, from injuries to loss of performance.
"Players like Ginter and Zakaria will always find a contract somewhere, that's clear. But the two of them don't want just any contract, they're ambitious. And I don't just say on an economic level, also from a sporting point of view. We will continue to talk to them and offer them what we can. I am still confident.
“I reiterate our intentions: we want to renew with them. But I can't rule out anything these days."