Sam Johnstone
The young English goalkeeper has been on loan at Aston Villa since January 2017 and has quickly taken up the mantle of first-choice keeper there. During the first part of the season he was the third choice first-team goalkeeper behind Sergio Romero and David De Gea, as Mourinho always prefers to have three keepers available in the squad at all times. Sadly he got no opportunities to play. But once Joel Castro Pereira was recalled from his loan in Portugal, Johnstone was free to go and get some playing time.
The 2011 FA Youth Cup winner, under the tutelage of Steve Bruce, has put in good performances while keeping clean sheets and helping his team improve its position in the Championship. This will only help his development with regular top-level games under his belt.
Next season could be make or break career-wise for Johnstone. The keeper situation at United seems to be very stable and it looks unlikely someone will rise above the top two choices. Hence I believe a permanent move away from Old Trafford would be the best bet. If he keeps working hard, he could easily become a Premier League quality keeper.