I totally agree with gcoe. Get your under grad degree first. To understand the possible underlying causes of any problem one needs a well rounded understanding of the body and disease process. I some countries such as Australia and Canada, the applied physiology and biomechanics part of the course is so robust that you will already come out with enough understanding to work with elite level athletes. In the UK they have a long way to go but they are getting there in some schools. Study is sometimes not enough. To be truly great I think to need to have a passion for the sport you work with from the ground up. i.e. to be a Ballet physio you need to know the forces on the body so you need to have at least taken part (even if for fun) in a few classes and tried a few turns etc. In football you need to have played a little at least.

A masters in something like applied biomechanics or in applied physiology (or something that combines both) would be great but nothing helps like getting in there and getting your hands dirty. Perhaps so come coaching courses during your PT degree. I did triathlon and swimming even before the physio degree and used them as a means to part-time work and $$ whilst studying. Swimming coaching is always a great one that will help you understand working with athletes and you can begin to do some experimentation with forces, biomechanics and heartrate type training.

Most of all keep up the enthusiasm.