I don't think football players work as hard as they do to get those multi-million dollar deals to not spend the money and just invest so they never have to do something again. (that would also go against the work ethics it took to get those contracts)
I don't blame them either. Spend the money. As a professional athlete, they've already put in more work than most human beings just to reach the professional level. Earn that extra money while you can, as a pro athlete, only the absolute best get 20 years, the large majority don't even reach "millions".