Alright this is a topic I delved deeply into when I had a LCL tear doing jiu jitsu. I was fully recovered 3 months later and squatting near my max. There's a good book out there by Lyle MacDonald called "Optimal Nutrition for Injury Recovery" that I referenced pretty often. I'll try to summarize it from memory here in order of importance:
1. Most importantly, eat enough calories (don't diet or cut). Make sure insulin and IGF levels are high enough for anabolism/repair. This means good levels of all macronutrients. Low calories means bad hormone levels.
2. Shoot for the higher end of protein, up to 1g per pound of bodyweight. This seems like a lot but it's easy to accomplish by addding one or two protein shakes/supplements per day.
3. Stay active and strength train with your uninjured leg. Studies have shown that you can limit the amount of muscle and strength atrophy achieved by the injured leg (or any body part) by training the uninjured leg. There are a lot of single leg variants of exercises (leg press, leg extension, leg curl, etc.) that you can still train unilaterally.
4. Supplements. If you're eating a lot, you should be okay, but if you want to be more thorough, make sure to get enough vitamin A, B complex, C, D, zinc/copper. Bone injury healing has additional nutrient requirements like calcium, vitamin K, magnesium, silicon and boron. If you really want to get optimal, then supplementing with glutamine a few times per day can increase muscle recovery.
5. Modulating inflammation. This one is a bit controversial since it goes against traditional (and some would argue outdated) models of injury treatment. The traditional model has you treating pain symptoms by using things like rest, ice, and NSAIDs (anti-inflammatory pain killers) after inury. While there's something to be said about preventing runaway inflammation that may be damaging, treating inflammation (nature's repair mechanism) as an enemy can slow down the recovery process.
I fall in the camp of believing that modulating inflammation is preferred over eliminating it. This means not using NSAIDs, not using ice but sometimes using heat, and not resting but getting the injured body part active asap. The problem with this is that what amount inflammation is appropriate for each individual widely varies. It's important to know your body. Supplements like fish oil, curcumin, green tea, white willow, and bromelain can be helpful in modulating inflammation.
