BBC Sport reported in July how Liverpool were considering a deal for Isak worth up to £130m.
Newcastle have maintained he is not for sale this summer, but that has not prevented Arne Slot’s side from taking a major interest.
The Premier League champions made an approach to Newcastle last month before lodging an official bid.
Boss Slot has already made a number of additions to his squad during a heavy summer of spending by the Anfield club.
They have signed Florian Wirtz, Hugo Ekitike, Milos Kerkez, Jeremie Frimpong, Giorgi Mamardashvili and Armin Pecsi for a combined total of about £265m without add-ons.
Meanwhile, the departures of Luis Diaz, Jarell Quansah, Caoimhin Kelleher and Trent Alexander-Arnold have recouped an initial £115m.
