Nightfall87: I heard that this turned up to be quite a problem at the Olympics. Since around quarter of an athletes are Muslims. For them this can not only influence their results, but also seriously damage their health.
wormholewizards: They can skip fasting, but they must replace it at later date. Doesn't mean the replacement must be in ramadan, they can do it in other months too depend on the condition.
Marouane Chamakh, Fredrik Kanoute, Bacary Sagna, Abou Diaby, Armand Traore, Samir Nasri, Hasan Salihamidzic, Adem Ljajic, Toure brothers, Sulley Muntari, all of them are Muslim footballer and play at top European League. Some of them skip fasting 3 days a week during ramadhan including matchday, and replace it later. Some of them choose to fasting even though on training and match day (Sulley Muntari) because they believe everything is on their mind.