The Chile international has only claimed one goal and one assist in 10 Red Devils appearances since his highly publicised January switch to Old Trafford.
Sanchez was again underwhelming on Tuesday night as United put in a sub-par performance to exit the Champions League at the hands of visiting Sevilla.
"Sanchez looks like a shadow of his former self," Ferdinand said on BT Sport after United's 2-1 defeat. "When he was at Arsenal he was a player everyone looked to for inspiration.
"Here he just looks like a stranger in this team. When you go to a [new] team you don't lose all of your talent, it's still there.
"In some ways I feel sorry for him but it just isn't going for him or other players as well. You could name the whole XI today, they were shocking."
United are next in action on Saturday as they host Brighton & Hove Albion in the FA Cup quarter-finals.