I toasted my calf muscle doing the first RO of the day in warmup. Landed the rebound and it went "pop". I couldn't walk proper for a month. Thankfully it was for Spring training, but my tumbling still wasn't up to its usual level by Aug tryouts because I wasn't able to even tumble until 2 weeks before. My coach knows my abilities and that helped put me on the team. It would for sure be harder with a kid you don't know as well.
Honestly, with a large group of kids at tryouts, if I didn't know that kid well, I'd probably place them on a lower team with the option of crossing over to a higher one if they could. If I knew the kids well, and knew what they were capable of, then they might still make the team depending on their injury.
To quote John Lennon, "Life is what happens to you when you're busy making other plans". Injuries too.