Did my knee in running years ago.
Just felt like a sudden sting and that was it, did hurt after the sting so I just carried on but after a while it started to ache so I limped home like a wimp. Next morning I could hardly walk on it.
Being a northerner of a certain age I just toughed it out and got on with my life but I had to stop sport for several weeks.
In the end I got myself a knee brace with jointed metal bars to the sides, so I could bend the knee but it prevented it from lateral movement.
Played for a couple of years with it like that until one day one of the hinges snapped and I just threw it away and carried on without it.
No idea what my knee problem was, it can't have been anything serious - and it hasn't really bothered me since although I did have an ache in it for a month or so several years after - and similarly that went away on its own and never returned since.
Another injury I received was when I went in very hard on a first tackle (always clatter your opponent at the very first opportunity and usually they keep away from you after that - so you know if they are on the ball they will be looking to pass so I'm not likely to need to tackle and more likely to stay on my feet and look to possibly intercept their pass if I could) and somehow pulled a muscle between my ribs.
Didn't seem much at the time but after the game and when the adrenaline wore of I was in agony for days afterwards every time I laughed, sneezed took a big breath or anything else really - surprising how often you uses those muscles you never knew you had!
Again I just toughed it out and let it heal by itself - like any true northerner would!