The on-loan Liverpool striker collided with United keeper David de Gea at a set-piece on the stroke of half-time and Ferguson feels referee Lee Probert did not react strongly enough.
"I think it's obvious, I don't think we need to dwell on that, it's an obvious red card but the referee has seen it differently,” he told Sky Sports 2.
"We know how they play, the ball is in the air most of the time. You've got to defend those things and they're very, very aggressive so you hope there's a strong referee. I'm not so sure we got that tonight."