Magpies boss Eddie Howe told reporters after allowing Isak to skip a 4-0 defeat to Celtic: "I chose to send him home. The last thing Alex wants if he is not playing is to be sat in the stand and under that scrutiny, then if he wasn't going to play today, we mutually agreed he shouldn't be here.
"It was my decision. He travelled back to Glasgow with us, but I decided to send him home due to the speculation around him. Both [Joelinton and Isak] are fit but not ready to play. Alex has trained and is fine but we didn't want to take the risk with him.
"Yes, I've had discussions with him, but that's not abnormal. I respect a player's career and how short it is. Alex has been really good, he's trained really well and I realise there'll be noise around him.
"We have a few of those players who are irreplaceable. Your top players are so hard to find, so hard to recruit and so hard to develop. So when you have them, you need to treasure them. Of course we're desperate to keep him as part of our team.
"I think it's difficult for me to ever give 100 per cent clarity on any player, I'd never do that. All I can say is Alex is happy at Newcastle, he loves the players, the staff, the team. I've never had any issue with him and I'm confident he's going to be here at the start of the season."