Spanish giants see the Swedish hitman as a potential long-term replacement for Robert Lewandowski.
And they believe Newcastle could be tempted to sell because they face having to balance the books to satisfy FFP and PSR rules.
It’s believed Isak, 24, would cost around £90m – but Barcelona would be prepared to try and strike a deal.
Our source said: “Isak is emerging as one of the best strikers in Europe, and Barcelona have been scouting him since Christmas.
“They see him as a player who could come in and lead their line for the next three or four years and be a massive success.
“He has all the attributes and would be a superb signing.
“Although Isak is happy at Newcastle, the chance of a move to a club like Barcelona would be very difficult to turn down.
“Newcastle know they will need to raise funds in the summer which is why Barcelona are ready to make their move.
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“And, at 24 years of age, his best years are ahead of him.”
But the Spanish giants aren’t alone in targeting the forward.
Arsenal are also monitoring Isak, as they look to bolster their forward line for next season.
A poor week saw the club knocked out of the Champions League by Bayern and lose ground in the title race after losing to Aston Villa.
But the club returned to the top of the Premier League on Saturday with a 2-0 win over Wolves.
They could extend their lead on City to four points if they beat Chelsea tomorrow, with Manchester City not playing until Thursday.
The Cityzens would have two games in hand, however.
With Arsenal potentially coming up just short in the title race in successive seasons, a striker is seen as a top priority – with Isak among the club’s top candidates.
He was heavily scouted by Arsenal before his move to St James’ Park in August 2022 for an initial £63m.
