My right leg "locks" when I ride my bike......?

My right leg "locks" when I ride my bike. My right leg is also thiner and marginally less-muscular than my left leg. Could this be the reason for it locking? What are other reasons? Please list your reasons. However, more importantly, I need to know how to prevent it. This is driving me mad. I don't think it's normal. All, please help with viable and optimum ways to prevent it. And, no, I have not seen any type of medical professional about this. Thanks.