Did my quad today whilst sqautting. Second time in 2 weeks, though first time wasn't nearly as painful. I had absolutely no pain before I started and always do a thorough warm up and stretching routine before starting so I'm sure it's not related to that.

At the bottom of the movement whislt squatting just when I start to drive up it feels like something snapped in my left quad. Now it feels like every time I go too low (sitting/standing up) and the muscle activates there is a knife being dragged down. Originally I though it was muscle related but it seems to be underneath the muscle on the front of the thigh towards the top. Thinking it might be ligament or even nerve related... The weird thing is I can walk with very minimal pain and flex the muscle to a degree.... suggestions??