Kostic is being targeted by West Ham this season and the Hammers have already made a bid for the services of the Eintracht Frankfurt star.
The bid was €15m, including bonuses, but it was refused by the German club, who want a sum in the region of €20m, and West Ham are still in negotiations.
Kostic’s contract with the Europa League holders ends next summer and it enables him to sign a pre-contract agreement in January.
He is eligible to sign it just four months from now, albeit with a non-German club, and the possibility of that is weighing on Kostic’s decision this summer.
The midfielder has already turned down offers from two Champions League clubs this summer but his coming to West Ham is not an improbability.
It is claimed West Ham would still need to sell Kostic on a move to the London Stadium but he would at least consider the Hammers if an agreement can be reached.
Time will tell if Kostic does end up moving this summer to West Ham or if he decides to wait until he is eligible to sign a pre-contract agreement to choose his next club.
He is aware that his next move could be his last big one given his age and will have to weigh how much he could earn as a free agent next summer.
