Speaking to Sky Sports, Guimaraes said: "What we know about Isak is he's injured and not been training with us for five days. He stayed [in Newcastle] to make himself better. He's there with a small injury. Of course, he's a top player, we know everything going around him.
"We want to keep our best players. He's a top striker, his last season speaks for itself. A top player, but as far as I know, he stayed because of his injury. We know the situation behind him but it's not for me to speak about him, it's something that the club will take care."