Time to call for mythbusters. I don't think that the ball and human leg contained enough physics to break another human leg. More or so with the newer and more lighter balls to come every year.

Not necessarily. Newton's 2nd law Force=(m)mass x (a)acceleration. While lighter and bouncier ball has increase in a but it is compensated by the lack of m, therefore the Force might still be the same. The only way to increase the Force is by using 12kg bowling ball on football matches .

Maybe all future footballers should wear helmets like Cech.