I don't think you can generalize on this. It all depends on the individual athlete. I knew several money-sport athletes who faithfully attended classes and I knew several who rarely showed up.
My very first class of my freshman year found me sitting in a Political Science class when (huuuuuuge Pitt football player who ended up starting for an NFL team) came in and sat down behind me. While I was trying to listen to the professor explain his grading system ("...attendance is mandatory, ladies and gentlemen"), I felt a *twang* on my back and realized that he was snapping my bra strap! I remember sitting there mortified thinking, (huuuuuuge Pitt football player who ended up starting for an NFL team) is snapping my bra strap! Do I get up and move? Do I turn around and slug him? Do I sit in the back row next class? Do I get his autograph?
Turns out I didn't have to worry about any of that since I never again saw him in class except for the midterm and the final.
