#2 Eric Bailly
Bailly was the first player signed by Mourinho at United. The Ivory Coast center-back was signed from Villarreal with a lot of expectations and featured in 38 matches for United in the first season. However, since then, he has only played in 25 matches for them in one and a half seasons and is going to leave the club in January.
Bailly is a young centre-back and an able tackler and marker. Moreover, he is strong in the air too and should have been the first choice centre-back for United. However, veteran Chris Smalling and Victor Lindelof have been playing as center-backs for United and Bailly has made only seven appearances for them in the ongoing season.
Mourinho should have helped him develop into a better defender and used him in the central defence for 7-8 years at least. Instead, he would move into another club after two and a half seasons with the club, a considerable part of which was spent warming the bench.