The Feyenoord boss has conceded defeat in the Eredivisie title race this season, praising the work of his counterpart in creating an indomitable side
Frank de Boer's men currently sit five points clear at the top of the table, and while the legendary Dutchman is pleased that his side remain in contention for second place, he feels the champions' form means the summit of the league is already beyond their reach.
"They are so strong and so stable that I did not expect it to go wrong for them," he told Voetbal International.
"I think congratulations are in order. They were the best this season, the most complete. De Boer did a great job and for that you have to show appreciation.
"[If we finish second] we will have succeeded in playing at the top once again, even having lost important players. Our performance has improved since last year. But, for sure, we will not be champions."
Kolbeinn Sigthorsson, Christian Eriksen and Derk Boerrigter all scored for Ajax in the Philips Stadion victory last Sunday.