Depends on which ligament, too. I have both knees unstable (decades of activities not helping them), inner straight one was partially torn last January when skiing hard. Knee bent to outside. I was barely walking, but took fixed gear (front brake, easy 50x19 gearing) to build up the strength without affecting bad (or worst) ligament.

It worked, I can practice my martial art again and I am planning to go skiing soon. I was also helped by acupuncture and koho-shiatsu.