Knee hurts when i try to straighten it and put any pressure on it

Patient: Hello, i was wrestling this morning and came out of it feeling fine and walking fine, a few hours later i notice my leg start to hurt, as they day went on it has gotten worse, i cannot straighten it without the pain becoming even worse and it hurts when i put pressure on it, it hurts mainly around my knee area and behind my knee but doesnt hurt to touch, any advice welcome, thanks