Newcastle, at least publicly, have maintained that Isak is not for sale and Howe said at the weekend he remains “confident” the player will still be at the club at the start of the season.
“I think it’s difficult for me to give 100% clarity on any player,” Howe said after their defeat by Celtic.
“Alex is happy at Newcastle. He loves the players he plays with, the staff, the team and I’ve never had any issue with him.”
BBC senior football correspondent Sami Mokbel reported last week that Liverpool’s pursuit of Isak “suggests they have had some private encouragement” and their interest in the Swede is likely to remain.
Meanwhile, defender Lewis Hall has not featured since February with a foot injury but has been included in the Newcastle tour squad as he steps up his recovery before the new season.
Newcastle face Arsenal on Sunday 27 July in Singapore before travelling to South Korea to take on a K-League All-Star team on 30 July and Tottenham on 3 August.