The 23-year-old striker added a further two goals to his tally as the second tier's in-form side claimed a comfortable 3-0 win over the Blades at Craven Cottage, with Fulham skipper Tom Cairney claiming the other.
Mitrovic moved to West London on a half-season loan deal in February after finding game time hard to come by at Newcastle United in the first half of the campaign, and now has five goals in his last four Fulham appearances.
"He shouldn't be playing in the division. I don't want to get too controversial about it but he should be playing in the Premier League. He should be playing at Newcastle," Wilder told reporters after last night's game.
"Mitrovic is an outstanding player and thankfully we won't be playing up against him in the next 11 games. We're always disappointed when we lose, but this is high-end, top-quality Championship football we're playing against. We have to learn and be better and hopefully enjoy the experience.
"I'm not complaining about what we've got, but Fulham reportedly turned down £15m for Cairney in the window. That's a good position for a club to be in, isn't it? To keep hold of their best players. I'm taking nothing away from them and the manager, who's a real good guy. This is a club that can attract the likes of Mitrovic and have the ability to keep hold of the players who have been in the headlines recently."
Mitrovic reportedly had loan offers to join Bordeaux and Anderlecht in the transfer window but opted to move to Fulham after chatting to manager Slavisa Jokanovic on Snapchat.