Louis van Gaal's side took the lead through Memphis, but goals from Sisto and Onuachu gave the Danish champions a first-leg victory, ahead of the return fixture at Old Trafford.
Manchester United slipped to a 2-1 Europa League last-32 defeat to FC Midtjylland on a miserable night for Louis van Gaal, who also lost goalkeeper David de Gea to injury.
The visitors’ preparations for the game were disrupted in the warmup when De Gea limped out of proceedings and was replaced by Sergio Romero.
The goalkeeper was certainly kept busy in the first half, making a crucial save on 36 minutes when a quick break left Kadlec clean through on goal, and with Hassan for support, but unable to beat Romero.