The teenage France international is a favourite of Real coach Zinedine Zidane.
Jonathan Barnett told Goal: "Real Madrid is a great club, a great club to play for.
"Eduardo will have a lot of clubs to choose from if Rennes decides to release him. They will be one of four of the five clubs in the world he could go to.
"Eduardo would love to play for a top club. Madrid are one of those best clubs in the world, as are Barcelona.
"If he will cost more than €50m? I think so."