The Swedish forward is one of the most in form players in the Premier League at present.
Amid rumors of Arsenal and other teams being in the hunt for his signature, Alan Shearer wants to see his old side retain Isak.
“No, is the answer,” Shearer told The Rest is Football.
"Who are they gonna go out and get that would come into Newcastle and do a similar job? We know that centre forward is the most important position.
"He’s one of the reasons they’re sitting in fifth and in the semi-final of the Carabao Cup. You could go out and spend £50-60m on another striker but who? What? Where. They are really difficult to find.
"So when you’ve got a b***** good one, why do you want to let him go for any price? If they’ve got to sell for PSR (Profit and Sustainability rules) reasons, there would be other players I’d sell before I’d sell Isak for £150m."