Isak has been among the goals in preseason for Newcastle.
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And Krafth told the Athletic: "I expect him to score at least 25 goals this season, maybe 30. He is a fantastic player.
"It is so difficult to take the ball from him, he is very good with his feet and a good goalscorer. He is one of the best players in the world at the moment."
Krafth's deal with Newcastle runs to 2025.
He said: "I know what I am capable of. Everyone here is really good players and everyone wants to be part of the team this season.
"I want to stay. I love being at Newcastle and being part of the team. I will work as hard as I can to make it happen."