Butt, a member of United’s legendary Class of 1992 and Treble winning squad of 1999, spoke about suggestions that Rashford did not care about the club or his performances.
The forward has come in for criticism since his poor campaign last term and slow start to this season.
“It's actually sad watching that because I've known Marcus since he was probably eight and nine at Man United coming through and he's always been the one that you hold hope for," Butt said to talkSPORT.
“I do believe and people will be screaming down the phone now probably but I do believe he's still got the talent to be one of the best top players in the world. He's just not clicking for the last few years at Man United, you're always saying he's just going to do it, he's going to do it but it's looking like maybe it's time for a change for him.
“No one really knows what his mentality is, but there's a lot of talent within that man and he's a top, top footballer. But it's just not happening for Man United now, people always point to the fact of his body language, he doesn't care, I can tell you now he does care, he's a proper lad.
"But it's just not clicking for him. Maybe it is time to go and find a club where he can get a bit of a deep breath, the eyes aren't on him all the time. He's the excuse for all the fans, all the fans look at him and it's not just him, the whole team, the whole squad needs to up the game.”