The Belgium international became the Premier League champions' only major signing of the transfer window for a £27m fee from Everton.
"He's got great potential, and if he's consistent with his best level, he will be a fantastic signing," Henning told MUTV.
"He can play so play different positions, he's a good footballer but there's something about him.
"He can get players around him, he can control and dominate games, and I think United have too few players who can do that. That's why I think he will be a great signing."
Fellaini worked under United manager David Moyes during the Scotsman's tenure at Goodison Park.