Are the doctors right?

on thursday i was playing football and i play in goal it was one on one i went in to the player and it was there knee or foot or something but it went into my knee, it was a very hard impact and my knee ballooned up straight away, and i couldn't move it and was in so much pain that they had to ring an ambulance there was a 5 hour waiting time in hospital and they were just trying to get people in and out as quick as poss, i had an xray they said i hadn't broken anything, and he gave me crutches and said i had sprained my knee cap, when looking on the internet it says that in order to sprain your knee u need to have over stretched but i didn't, i still cant move it, it is extremely painful and cant put any weight on it. is the doc right ? if so how long am i likely to be out for?