Wow. Nothing like choosing an easy case to start with. Good for you!
Is the tear partial or complete? If complete, is surgery an option?
Assuming surgery is not an option, and that maybe it's severely torn but not completely ruptured, you've got a decent shot at things. Here are the things I would try:
1. A chiropractic or osteopathic evaluation. This is essential, even if it takes you a while to source, as the spondylosis has very likely created some nerve root impingement and secondary weakness that will frustrate your attempts to strengthen the leg. Try for a vet, but if there isn't any local expertise, try to round up a human practitioner that is willing to let you walk them through the anatomy, if they haven't done it before. If they use an Activator, everything should be safe and fine. The practitioner should also be able to make sure that there is no S-I joint fixation masquerading as a torn cruciate, which happens all the time.
2. Your two general differentials are stasis in the GB channel, or Blood stasis in general. For Blood stasis, look for heat at ST 37 and BL 17. For GB channel obstruction, look for heat at GB 34, 40, 41, 27, 30, and even potentially 25.
3. If Blood stasis, and the dog appreciates warmth, use Xiao Huo Luo Dan. If the dog is very hot, try Xian Fang Huo Ming Yin. If it's a GB case, try Xiao Chai Hu Tang, with Qin Jiao added for best results.
4. Regardless which formula you use, pick up some Ruta graveolens 30C (a homeopathic) and use at least once daily.
Your timeline for improvements will be slow, unless there are vertebral fixations that are creating nerve root impingement, or there is an SI joint fixation. Otherwise, some patience will be required. Dogs that are badly affected can take as long as six months to be lameness free.
Hope that's helpful advice. Best of luck to you, and no worries using the above advice in a cancer case. There's no risk of spreading the tumor.
All the best,
Steve