But Zoran Filipovic, who worked with Grujic when he was technical director of Serbia, believes the midfielder should stick with Sergio Conceicao's side.
“I've been following his season. He's a player with great talent. He's evolved a lot since leaving Serbia," Filipovic told Record.
“He's adapting to big clubs. I think he has a great future ahead of him. He can evolve a lot because he has quality for that. I think he'll improve a lot.
“I think it'd be better for Marko to stay at FC Porto. I think the bad thing about Serbian players has been the fact that they leave their country very early to play in very big clubs, where it's very difficult to play because of the competition.