Ajax coach Frank de Boer says he's losing Jan Vertonghen just as the penny's dropped.

Newcastle United, Arsenal and Tottenham are all chasing the defender, who has declared he'll leave Ajax at the end of the season.

"I think Jan over the last few months has been playing incredibly well," said De Boer. "He has now seen the light, something we have always hammered home. Not only within but also outside the field.

"His development is very beautiful to see. I have been very critical of him and maybe he was angry with me. But ultimately I think he understands me."