After Matt Targett, Nick Pope, and Sven Botman, the 22-year-old is the Magpies’ fourth summer signing.
Isak has nine goals in 37 international appearances for his country and 44 goals in 132 games for Sociedad.
It was a significant choice for him, but he was pretty pleased with it.
“It is a fantastic, storied club with incredible supporters, and I believe anybody would want to play for them. They were a significant factor in my decision to come here, as was the club’s vision, which I firmly support.
“You should always enter a team knowing how they operate. I find Newcastle’s brand of football to be incredibly appealing, and I want to be a part of it.”
Given Callum Wilson’s history of injuries and his current hamstring ailment, Newcastle’s offensive options are improved by adding Isak, a former Borussia Dortmund player, to St. James’ Park.
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Eddie Howe, manager of Newcastle, said: “Alexander has decided to join us, and I’m pleased about that. He has exceptional skill and the potential to benefit the squad significantly.
“He has a variety of qualities that will complement us and is technically extremely strong, but he is also in a fantastic age range to develop with this team.
“Alexander was brought to Newcastle by the club’s owners and the transfer committee, for which I am grateful. Everyone here is thrilled to have him on board.”
Wilson, 30, will be out “for a few of weeks,” according to Howe, who earlier on Friday described his hamstring ailment as “not severe.”
According to Howe, Martin Dubravka, the goalkeeper for Newcastle, was not reported in transfer discussions with Manchester United.
After Nick Pope replaced him as the club’s top player, the Slovakian has been mentioned in reports as interested in a transfer to Old Trafford.
Howe stated, “I don’t believe he’s in negotiations with Manchester United.” “Although there has been communication between the clubs, it is likely that this will continue, as shown by the conversations.
However, I’m incredibly hesitant to lose any significant players to the group, so it’s a choice that will be made without my input.