The complication comes when no one comes in for him, and he doesnt indicate a willingness to sign a deal.
What then? Do we sell at a reduced fee? Or gamble on convincing him to stay and risk losing him on a free? (ditto Eriksen)
If no-one comes in for him now it won't be because of the fee so selling later at a reduced fee doesn't seem logical and my best guess is he'll leave on a free at the end of the season. Getting a whole season out of him could work out better financially for Spurs than letting him leave in January for 15m.