Danish newspaper Ekstra Bladet says the youngster has agreed personal terms with the Dutch side.
“I’m glad that a decision has been made about my future. It’s a huge challenge for me to join Ajax and I’m really looking forward to it,” the defender was quoted as saying.
Ajax are yet to agree on a deal with Brondby for the 17-year-old, who is expected to join the club on January 1.
Manchester United, Chelsea and Milan were also reportedly keeping tabs on the defender.