Might want to drop regular squats for awhile, not always for everyone with regards to quad/leg development. Try a different approach to leg workouts.
Might try:
1) Front squats..elbows held high up for better balance. Option is to have the heels on a 2" block, BB plate, etc...
2) BB Hack squats...heels on a 2" block or a pair of 45's, etc.
3) Step-up's...helps to insure balance of development between the right & left legs. Step-ups are not the same as one legged squats, though both has it's place in an all around leg program. Could also consider Bulgarian squats.
4)Sissy squats.Very affective for an ultimate stretch for the quads and added muscular size. Last exercise done on this program to fry the quads.
2 sets each of 7-12 reps
Ham's
1) GoodMornings...keeping the spine and back straight throughout the movement. Will limit the distance of the stretch but can focus more of the Ham's themselves. Can also raise the toes on a 2" block for an added stretch.
1) Lying leg curl-manual resistance...one leg at a time. Lay on a higher bench and have a training Bud apply resistance as you attempt to curl the leg up and all the way to the butt. Can also have the person helping you use a long folded towel rather than the hands.
2 sets of 7-12 reps. Good Luck.