Any tips for training legs in such a situation?
I'm also trying to recover from a knee injury.
Yes start with an elliptical bike 20 minutes a day. Then start walking if you can 1 mile 2 miles just enough not too much I had access to the beach and the sand is not as harsh as pavement so be aware if issue. Then start doing leg extensions and hamstring curls. Eventually start doing bodyweight squats once you have strengthened the connective tissue. Also keep reps in the 25 range on all of this do not go heavy.
The elliptical bike is where you will get the strength you need to do this for weeks before you start doing extensions and curls and you need to do those for a couple weeks before starting the bodyweight squats. Keep the weight light do sets of 25 do not strain take it easy. The bike gets the fluid out you have to have the fluids out before you start lifting. If you start to get fluid after lifting take it easier the idea is to do enough to stimulate without causing further injury. My knee arthritis has almost completely disappeared following this protocol
I also do not take any NSAID as bad for stomach I take no medication for my knees