I want an 18-year old hockey player to believe his hockey career is over due to injury. But I want him to be wrong. He would have gotten excellent medical care from the start, so it can't be anything like a treatment he just wasn't aware of. I think it needs to be something that heals up way better than he expected. I think I could work it that it's was just a very hard-to-recover-from injury, rather than an impossible-to-recover-from type. Does anyone have any ideas for an injury that would have seemed career-ending for several months but that would then turn out to be not really that bad?
A knee injury could work... the doctor could tell him that he's got a torn ACL/MCL and he wouldn't be able to play again, but it turns out that it was not as bad as first thought. There are three or four degrees of "torn ligament", ranging from "requires some physical therapy" to "we've gotta swap it out for a new one".
You might go with a brand new technology or surgical procedure. Things like that take time to disseminate. So one provider might be aware of it after two or three had said there was nothing available. What body part? Pick one then do a PubMed search for new treatment.
Take a look at the NFL. They have recently developed new treatment options for torn ACL and the injuries went from career ending to season ending (sometimes). However, there have been a few exceptional individuals like Adrian Peterson who had a serious injury and seemingly miraculous recover. Probably a lot of good stuff to look into with his story.
The first thing to come to my mind too is a knee injury (ACL/MCL) which is definitely bad, but so common. Another tough injury that would be career ending yet difficult to come back from but possible would be a neck injury. Less common than the knee injury but could make for an interesting story.
That's what is have. My knee is better then I expected but still hurts with bad weather or being overworked.
I remember a few years back when Marc Staal took a slap shot to the eye, think he tore his retina and fractured something (pretty hazy) but quite a few people thought he'd never be able to see again from that eye let alone play hockey. But he made a full recovery about a year later and started playing pro hockey again. You could look up potentially career ending NHL injuries or KHL (there have been lots there) to get some ideas.
A brain injury could also work, if you want to go that route. It's notoriously tough to predict the outcomes from brain injuries in the early stages of recovery, and a lot of doctors err on the side of preparing patients for the worst outcome rather than raise their hopes and have them disappointed.