Treadmill
Have one leg on the edge of the treadmill and have the left leg on the treadmill belt. Put the treadmill at a low speed, i recommend 3 mph, and have the left leg walk on the moving belt, while the right leg stay on the edge. lean your body mass on the right leg to keep balance on a non stationary plane, so the left leg feel secured moving on the moving belt. keep doing this exercise, until you feel any tiredness in your left leg