Vertonghen has a year left to run on his Ajax contract and boss Frank de Boer has admitted he is now ready for a move elsewhere after taking his game to a higher level this season.
"Jan has seen the light," said De Boer. "Not only on the pitch, but away from it. I have been very critical of him and, at some point, he must have become fond of me.
"His development is wonderful to see. If he leaves, I think it is right. Earlier, I thought it would have been unwise.
"It will not be easy to replace him."