Isak was pictured by Sky Sports returning to Newcastle's Benton base on Monday morning, with the striker having flown back into the region over the weekend following his stint in Spain, where he trained alone at his former club Real Sociedad.
Newcastle's squad landed back in the UK on Monday morning following Sunday's draw with Tottenham in Seoul, which brought to an end the pre-season trip to Singapore and Korea.
But the players who were part of that trip won't join Isak at the training ground today, with Howe instead giving his squad the day off after their long journey home.
Howe now plans to sit down with Isak and is expected to spell out his disappointment at the striker's conduct since he made his Liverpool transfer wish known.
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Asked on Sunday whether Isak would be returning to training this week, Howe told Mail Online: "You have to earn the right to train with us.
"We are [Newcastle United](http://www.thenorthernecho.co.uk/sport/football/newcastle). The player has a responsibility here to be part of a team and part of a squad - you have to act in the right way. So that is also at play here.
"We will make sure that any player does that to earn the right to train with the group. No player can expect to act poorly and train with the group as normal."
Howe added: "Of course I'd like him to be (there), but whether he will I don’t know at this moment in time.
"We have been here with the time difference, preparing for training and for games. Other people have been dealing with that situation back at home."
After making their interest in Isak known, Liverpool failed with their first formal bid for the striker last week, with the £110m offer falling significantly short of Newcastle's valuation of their star man.
Following that failed bid, Liverpool sources claimed the Premier League champions wouldn't be returning with any improved offers, but their interest remains and Isak wants to move to Anfield this summer.
But Newcastle won't budge on their asking price and won't allow Isak to leave until they have a replacement in place.
United are negotiating with RB Leipzig after tabling an offer for Benjamin Sesko, their top target, at the end of last week. Other potential targets have been identified, while Newcastle remain hopeful of a breakthrough in their pursuit of Brentford's Yoane Wissa.
Meanwhile, Newcastle are in talks with Burnley, who want to sign Martin Dubravka on a permanent deal.
Dubravka only signed a new contract in February but it was only a 12-month extension to next summer, and the arrival of Aaron Ramsdale has pushed the Slovakian back down to third in the pecking order.
Burnley are in the market for a new keeper after James Trafford returned to Manchester City at the end of last month.