Mitrovic was brought to Newcastle in the summer transfer window, and he was expected to be their main goalscoring threat.
However, the 21-year-old has not hit the back of the net with any regularity during his time at St. James’ Park.
Mitrovic has just three goals to his name so far this season, but McClaren insists that the striker’s effort cannot be questioned.
“Mitrovic was unknown and needed time to settle, and I think he’s been up and down," he said.
“(Ayoze) Perez can score. We expected Riviere to carry on but he’s been injured.
“Unfortunately, Papiss has been injured as well over various parts. At the present moment we have one recognised striker, which is putting a lot of pressure on him.
“It’s put added pressure on to Mitrovic who is a youngster who is coming into this league for the first time.
“I think he’s doing well, it’s just the end product and the finishing at the moment. But Mitro’s working damn hard out there."
Despite Mitrovic’s struggles in front of goal, he has still managed to win over certain sections of Newcastle’s support with his sheer commitment.
The Magpies are also attempting to take some of the goalscoring responsibility off his shoulders, by bringing in another forward in January.
Newcastle have been linked with a host of number nines, with McClaren eager to increase his side’s attacking threat.