Agent Jorge Mendes has not ruled out David de Gea leaving Manchester United for Real Madrid because of the way situations can rapidly change in football.
United manager Louis van Gaal has recently expressed his confidence that the Spain goalkeeper will resist Madrid's overtures and sign a new contract to stay at OId Trafford.
When asked about De Gea's situation on Thursday and the prospect of a switch to the Bernabeu, Mendes said according to newspaper Mundo Deportivo: "I do not know the future, things change every five minutes. We all know that in football nothing is impossible."
Mendes, agent to a host of world stars including Cristiano Ronaldo, was speaking at an event to launch his own autobiography.
He added of De Gea in Marca: "David is a Manchester United player and has a contract. You have to respect that."
De Gea, 24, is contracted to United until the end of next season.
At the same event, Mendes predicted former United man Ronaldo, who turns 30 next month, could play on for Madrid for another decade.
He said: "I am confident that he will retire at Real Madrid when he is 38, 39 or 40."