Magpies boss was at the Amsterdam ArenA to see Ajax beat De Graafschap with his sights set firmly on the Belgian defender, who is also on the radar of Arsenal and Tottenham
The Belgian has been monitored by Arsenal and Tottenham, and has expressed an interest in joining international team-mate Thomas Vermaelen at the Emirates Stadium. But Vertonghen also told Goal.com he believes Spurs is an "amazing club."
Vertonghen's contract at Ajax will enter its final year in the summer and the Dutch side are believed to be ready to cash in on one of their top players if the price is right.
Newcastle have also been linked with Twente centre-back Douglas and Erik Pieters, PSV's Netherlands international left-back.
The Magpies have successfully plundered the Dutch market in recent years, with key players Tim Krul and Cheikh Tiote signing from ADO Den Haag and Twente respectively.
Newcastle have also shown a knack for picking up affordable, top-quality signings from Europe in recent years, investing the £35 million they received for Andy Carroll on first-teamers like Yohan Cabaye, Hatem Ben Arfa and Papiss Cisse.