Yorke told talkSPORT via The Mirror: "You have to find out where the individual is at, what is going through his head, what is his thought process in his everyday life. At the end of the day, we all have issues, we all have tough times in our lives.
"I am sure that being left out of the England set-up last year, you expect him to come back with a little bit of fire in his belly and kick on after a poor season by his standards. Marcus Rashford is the only person who can get himself out of that slump. You can bring in the best coaches around him, but he has to have that burning desire to get himself back. We know he has all the talent and all the ability.
"But if he is not prepared to put that effort in and really bring himself back from his poorest season last year, he is not going to get back to that level. He has to want to do it. I have defended Marcus many times, but he just seems unhappy. For whatever reason I don't know, but just does not seem to be enjoying his football like he used to."