The 24-year-old, who missed the Magpies' pre-season tour, has only recently returned to Tyneside after training in Spain using the facilities of his former club, Real Sociedad.
His isolation from the main group is understood to be a decision made by manager Eddie Howe, following a 110-million-pound bid from Liverpool last week - an offer that was swiftly rejected by Newcastle.
The Premier League side are reportedly reluctant to part with their star forward, particularly in light of complications surrounding a potential replacement.
Newcastle recently submitted a 69.4-million-pound bid for RB Leipzig striker Benjamin Sesko, but the Slovenian is believed to favour a move to Manchester United instead. That development has made it increasingly unlikely that Newcastle will entertain further offers for Isak this window.
The situation puts Newcastle in a delicate position. While Isak remains under contract and continues to train, albeit separately, the ongoing uncertainty threatens to unsettle both player and squad.
With the transfer window still open, speculation over Isak's future is expected to persist, but unless Newcastle can secure a top-tier replacement, they appear determined to keep hold of the Swedish international.
Liverpool are reshaping their squad with high-stakes transfers, as Darwin Nunez's blockbuster move to Al-Hilal nears completion and Harvey Elliott edges toward a switch to RB Leipzig.
Chelsea are intensifying their pursuit of RB Leipzig's Xavi Simons as they aim to bolster their attacking options for the upcoming Premier League and Champions League campaigns.
Liverpool are reportedly plotting an audacious move for Paris Saint-Germain's electrifying winger Bradley Barcola, aiming to make the 22-year-old a cornerstone of their attacking rebuild.
Aston Villa are preparing for a fresh wave of interest in star striker Ollie Watkins, with both Newcastle and Man United monitoring the situation closely.
