It is my personal view, and i am not an expert either.
If you have much fat (boso) in your thigh, i think you can either go for surgery or exercise in Gym. Thigh exercise will burn your fat but you may see some muscle also.
As you already mentioned, you play sport a lot, running should help you to cut off some fat. As far i know, runners do not have big muscle but strong leg/thigh.
I recommend you to hike in uphill or run in treadmill with some incline. Run until you can not walk.

(If follwoing my idea is tough or problematic to your health, stop it and seek different way out.)
good luck