Ajax have already sold midfielder Frenkie de Jong, 22, to Barcelona in a deal worth 86 million euros (75.18 million pounds) with his 19-year-old team mate Matthijs de Ligt expected to follow him out of the club for another big fee.
Others like Hakim Ziyech, David Neres, Donny van de Beek and goalkeeper Andre Onana could move to some of Europe’s biggest clubs after the Dutch club's unexpected progress to the Champions League semi-finals.
“To say I fear the transfer window is not the right word but our players are hot right now,” Ten Hag told reporters.
“We left a very positive impression and that is a compliment for Ajax. It will be a heated summer, that we have to expect.
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"But the club’s leadership and I are of the same opinion that we must have the potential to try and achieve again what we did this season.”
An estimated 60,000 supporters gathered on Amsterdam’s Museum Square on Thursday to celebrate Ajax's domestic league and cup double, which was completed when they beat De Graafschap 4-1 on Wednesday to finish three points clear at the top of the Dutch league.
"It was an incredible season and we must continue in the same way. The enemy never sleeps," Ten Hag added.
"Next season it is going to be a lot more difficult than this season. To reach the Champions League semi-final and win the double – that was never a target. This season belongs among the best in the history of the club.
“To become league champions again will be our ambition. But in Europe? I cannot say right now. That we can only determine on Sept. 1 when we know what our squad looks like.”
(Reporting by Mark Gleeson; Editing by Toby Davis)
