The chatter intensified this week after Newcastle's attempted swoop for Eintracht Frankfurt striker Hugo Ekitike fell through. The deal - initially looking promising - collapsed by Thursday morning, despite being lined up as a potential club-record signing.
Howe is a long-time admirer of the Frenchman, but the failed move has sparked speculation that Ekitike was being lined up to replace Isak next summer.
Such claims have irked the Newcastle manager, who sees Isak as integral to the club's long-term project. Internally, suggestions that the Swede could be sold are viewed as premature and even defeatist.
Still only 24, Isak continues to improve, and the club is working hard to tie him down to a new bumper contract that would make him Newcastle's highest-paid player. The vacant No 9 shirt has been floated as part of the negotiations.
Liverpool and other European heavyweights have shown interest, and it's acknowledged that Isak may harbour dreams of playing for clubs like Real Madrid or Barcelona.
Offers above 130 million pounds could force the club's hand, but Newcastle's Saudi-backed ownership - via the Public Investment Fund - are determined to retain their top talent.
"It is a frustration because I don't see why our players are getting linked here, there and everywhere with other clubs," Howe said towards the end of last season.
"I'd like to think the players are happy here. I'd like to think again that they're seeing us grow and develop into a team that hopefully can compete at the top end of the division. We have no divine right to do that, but I think we're going in the right direction, so yes, it's a source of frustration."