I Was Skiing And Fell, I Heard A Pop On

I was skiing and fell, I Heard a pop on the inside of my left knee. I was able to walk with a cane. It was very sore for a week. I am now able run and play tennis with no problems. I still worry about it because if I put pressure on my left leg down by my ankle pushing outward I can feel a weekness in what I think is my medial collateral ligament. How can I tell if I need an operation?