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The striker missed the pre-season tour to Asia and has not featured in any of their friendly matches.
Isak returned to Newcastle's training facility earlier this month but has been instructed to stay away from first-team training by Howe.
Howe said: "We do [have to forget about Isak] - he's not here with us.
"We have to focus on who is here and get the best out of them.
Alex's situation has been unchanged for a while and that will continue to be the case."
Howe: Isak wouldn't be where he is without Newcastle
Howe has claimed that Isak knows he wouldn't have had the success he has without Newcastle amid the ongoing speculation surrounding his future.
Isak has refused to play for the club again following Liverpool's interest in the player, but Howe says he believes the striker knows how important the club has been for him.
"Me and Alex have enjoyed a great relationship.
Without his team-mates, without the supporters.
"He is a highly intelligent person and he knows he wouldn't have had the success he's had without everybody connected with Newcastle."
Newcastle expected to move quickly for Wissa!
Yoane Wissa is set to miss Brentford's clash with Nottingham Forest owing to transfer speculation
Newcastle are expected to move quickly on a deal for Yoane Wissa after Brentford complete the signing of Dango Ouattara, who is set to join the Bees from Bournemouth in a £42m deal.
Sky Sports News understands Wissa's representatives - who are in the UK - were assured Brentford would engage with Newcastle if there was movement on forward reinforcements.
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Brentford boss Keith Andrews confirms striker Yoane Wissa won't be in the squad for their Premier League season opener against Nottingham Forest
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