Stand with your feet flat on the floor at hip width apart.
Tie a resistance band into a loop around a secure object.
Place your affected leg in the loop, with the band behind your knee.
Step back so you have some tension in the band.
Keeping your body straight, bend both knees a little.
As you straighten your knee back up you will pull against the resistance of the band, working the thigh muscle.
Relax and then repeat.