The midfielder battled to compete in the 3-0 Champions League rout.
Fletcher said afterwards: "Man Utd are way off Man City and Liverpool but it's about how they bridge the gap now. Do they go down the route of recruiting the best young talent and try to mould them in the United way rather than buying ready made players who maybe don't have their heart in it?
"Scott McTominay did not stop all night and if you can put that work rate and attitude into players who have more ability, that would be great. Roy Keane and Paul Scholes had it but they were world class players as well."