Newcastle signed Mitrovic from Anderlecht over the summer, in a transfer valued at £12.5 million by the Telegraph, and he has made a huge initial impression at St. James' Park.
His bludgeoning style makes him an interesting striker to watch, and he gives Newcastle an excellent outlet, but he has been over-aggressive at times.
Mitrovic has already received one red card, and that total could easily be greater, given some of the challenges he has put in.
And Simpson said: "We have to do everything we can to keep Mitro on the pitch. He makes a massive difference. We were trying with Papiss [Cisse] up there, he’s a different type of striker – he wants things played in behind for him to run on to. He needs balls bobbling around that six-yard box."
Mitrovic's latest appearance for Newcastle came against Chelsea, and his passion for the club was evident throughout.
The Serbian international was visibly seen revving up supporters and teammates, but he was unable to inspire the Magpies to victory, with two late Chelsea goals meaning the final score was 2-2.
Newcastle's performance in the match was still much improved, though, and they will be relying on Mitrovic to put in a similarly impressive display against Manchester City this weekend.
The Magpies are likely to be on the back foot for much of the game, so they will need Mitrovic to hold the ball up and bring others into play when he does receive possession.