The defender impressed in a midfield role in the club’s FA Cup win over Blackburn Rovers on Tuesday night.
Benitez, without a number of midfielders, fielded Schar out of position at Ewood Park.
United’s manager, however, would rather the Switzerland international played in defence.
“No, he’s a centre-back,” said Benitez, who could have midfielder Mohamed Diame back for this afternoon’s home game against Cardiff City.
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“We were practicing for a couple of days in this position. In Germany and with his national team he played in this position. I knew he could play there.
“In a game like this where we play 4-3-3, we could play this way. He’s not a midfielder who can play with mobility, but he can stay there and pass the ball. After we changed again – 4-4-2 in the second half.”
Winger Matt Ritchie, meanwhile, has been fielded as a left wing-back in recent Premier League games.
“I said before that I try to maximise what we have,” said Benitez.
“Obviously, Dummett is injured, so we have to find a solution in this position and we’ve been looking for a left full-back for three years. Hopefully, we can find one.
“(Javier) Manquillo can play there in a line of four and we can play Ritchie in a line of five, because he’s not a full-back. As a wing-back, he has energy and he can keep the width of the pitch. He has some positives and some negatives, we know that.”