"Valencia is an old style winger. He's a real throwback," Morgan told the Manchester Evening News.
"I don't think he's the greatest winger in the world, but he's a handful and he wants to get to the by-line. He will always ensure that the opposition full-back has to curtail their attacking instincts.
"He's up and down that right flank all day and doesn't wander inside much which gives you constant width and stretches teams like he did at the Etihad. When you can spread opponents out like that it creates space for the likes of Wayne Rooney and Robin van Persie and you saw the value of that in the derby.
"Young doesn't always stick to the touchline, but when he does stay out there he causes the same problems. It's traditional United and is a great weapon. Having two wingers going at a defence is exactly what opponents struggle to cope with these days.
"Full-backs generally are not good defenders any more. They are not equipped to deal with marking an out-and-out winger these days. They are half-baked forwards. Any side with wingers who can play are a winning team as far as I am concerned.
"It was good to see United use them at City and they really did stretch them. It does beg the question as to why Valencia didn't play at the Etihad last April."