The 23-year-old striker has only made one Premier League appearance for Newcastle since their return to the top flight after being given a three-match ban for elbowing West Ham United's Manuel Lanzini back in August.
Mitrovic, a £13.5 million signing over two years ago, was eligible to start the Magpies' 1-1 draw with Liverpool before the international break but Rafael Benitez did not name him in the matchday squad in what might be the source of the rumour.
There is no doubt that the Serbian has plenty of talent but he continues to divide fans of the St James's Park club because of his behaviour.
As a result, some Newcastle supporters would not be against the prospect of seeing him leave the transfer window re-opens in January.
ask for 30m just like when they overpriced Konckaert when we wanted him— Ryan Smith (@Smithlaaar_) October 9, 2017
They can have him.— Eric Gibbon (@EricGibbon) October 9, 2017
Maybe they want someone else they can deny deliberately stamps on people.— Ahhhhhhhhhhh! (@Ahhhh_Rafael) October 9, 2017
— JOP (@40yearsofhurt) October 9, 2017
Mitrovic has all the attributes to be a top striker, just a shame his footballing brain/application lets him down on occasions #nufc— NUFC Review (@nufc_review) October 9, 2017
Hahahahahah— Robert Brown (@robbrown172) October 9, 2017
You can see why some United fans wouldn't be keen on the idea.
He might well be Newcastle's best striker as far as talent goes but time will tell whether he can displace Joselu - who scored against Liverpool - and begin playing regularly for Benitez again before January.