Not a football injury, but the worst injury I had was when I was 14. I raced BMX bitd and at one meeting on a very fast track, I got caught up with another rider 1/2 way down the first straight.
I landed with my knee bent on the upside of a jump, which because of the speed and force of the hit, split my kneecap in half.
Man that really, really hurt, I can still feel the pain over 30 years later.