#3 Matteo Darmian
Simply put, Matteo Darmian never amounted to anything at Old Trafford, despite various predictions that he'll become one of the best right-backs in the league. He arrived at Manchester United from Torino in 2015 for £16m and was one of Louis van Gaal's many questionable signings at the time.
Darmian featured in 28 games for Van Gaal's side in the 2015/16 season, but once Mourinho joined for the following season, his total appearances dropped to 18, cut by ten. For the 2017/18 campaign, it was cut by another ten, leaving him with only 8 appearances to his name. And lastly, this season, it's the lowest it's ever been at 5 appearances. It's clear he's no longer needed.
That's not to say that Matteo Darmian isn't a good player, because he is; he just doesn't fit the Premier League style. He's outmuscled far too often and the sheer speed of the league is too much for him to handle. He's likely to head back to Serie A and do well there, as the style of play is more relaxed and generally a lot easier.