Depending on your injury, you may still be able to do drills and technique repetition (no free rolling). But if you can’t train at all, there’s still a lot you can do.
99% of the time, when a student has a bad injury and can’t train at all, they don’t come to class. This is a big mistake!
I have a very good student who had a bad knee injury. He was a blue belt, but it wasn’t uncommon for him to catch purple belts. He was out for 9 months. When he came back, it took him 3 months to get his level close to where it was before.
In that same time period, another students had a rib injury. He couldn’t train (he said sometimes breathing hurt!), but he still came in and watched. He helped beginners, he watched what was being taught, he reviewed notes, watched youtube… when he got back to full rolling he had almost no rust!
I read about a POW in Vietnam that was held in a tiger cage for over a year. He was so bored that he entertained himself by visualizing himself practicing golf for hours per day. When he returned home he went golfing and played golf. His score was the same as when he left for war several years before!
If you have to take a physical break from Jiu-Jitsu, don’t take a mental break!