What if the young man has undiagnosed ADHD or a learning disorder. I remember a story about former NFL great DT Pat Williams. He basically couldn't read in college which made him unable to get good grades or learn a playbook. He's a smart man so it wasn't intelligence that was holding him back. As it turns out he had some disorder that made it almost impossible to read off of white paper. They found out that he was able to read just fine off of red paper and he got good grades from then on.
Sometimes issues with grades are more complex than just either they aren't smart or they don't care. We don't know why a guy has trouble in school so a blanket statement about someone's intelligence without the full story is just plain not fair to that person.
Don't get me wrong, grades should be priority number one since most of these guys will need that education after football even if they are in the .1% that goes pro.