Jose Mourinho's team were dominant in the first half on away soil, but were on the back foot during the second and were eventually made to pay for it.
"It's not something you would associate with a Jose Mourinho team. They lacked professionalism and discipline in the second half," Ferdinand told BT Sport. "Wave and wave after attack was coming. It just wasn't good enough in the second half.
"Nobody likes losing and the manner of how they lost will hurt. When you have had a first half as convincing as that, to come out in the second half and let the game become so open, is not professional on their part.
"Manchester United will be bitterly disappointed because it would have been an opportunity to rest players in the last game."
The Red Devils need a point in their final match against CSKA Moscow to secure top spot in Group A.