According to a report by Dines et al, there are several studies which have concluded that the most common injury to the tennis player is an ankle sprain. One of the easiest prevention measures to take, and if you notice at the US Open this summer most professionals have them, is to utilize a supportive ankle brace while playing. This helps to support the ankle and can minimize inversion ankle sprains, which occur easily with abrupt stopping and change of direction movements. Other preventative measures can be taken including improving ankle and hip strength, as well as working on your balance. You can speak to a tennis professional or even a physical therapist in your area to get more specific recommendations.