The injury will not be treated with anything but ice and bandages put on by someone who is not a medical professional. I would have gone with a sprained ankle, except that I've both sprained and almost broken mine without having any problems walking on it (as long as you don't count the pain). I need an injury serious enough for my character to try standing on it and collapsing on the floor instead.
My character is a twenty years old singer in a band, not fit at all, a short, skinny wreak with tendencies to an alcohol problem. The injury might be caused by the jump, be aggravated from one he got a few days prior (either when he was beaten up or when he did some acrobatics on stage that went wrong) or be from wear and tear, since his job consists of a lot of heavy lifts and carrying.
How much will it hurt?
Will the knee/ankle be discoloured or bruised by this injury?
Will support bandages help at all?
Setting: modern time England
Searched: "knee injury getting worse" "injured knee from jumping" "injured knee from dancing", the same strings with ankles. Honestly I have no clue how to find what I'm looking for, and my slightly relevant search strings didn't give me what I needed.