Going into the game against United on Tuesday night, Mitrovic only had three Premier League goals to his name since arriving from Anderlecht in the summer.
McClaren felt a good way for the striker to improve his goal tally would be to take his side’s spot kicks, and the former England boss told Mitrovic to make sure he took any penalties they were given against United.
The plan worked, as the 21-year-old striker scored from 12 yards in Newcastle’s 3-3 draw against Louis van Gaal’s side.
And Mitrovic said: “I spoke with him [McClaren] before the game, he said that if a penalty comes if I play I need to take it.
“It is my responsibility in this team to take the penalty. I take the ball and I score the goal and I am very happy.
“I was really happy and I am really happy now."
Mitrovic also claimed two assists in his side’s match against Manchester United, and he proved to be a threat throughout the contest.
The Serbian international’s physicality proved very difficult to deal with, and United’s defence never got a moments peace all night.
Newcastle’s draw against the Red Devils has seen them move to within one point of safety, and stopped a run of four straight defeats.