i know many doctors simply tell you to rest. you should definitely listen to your body and not do anything that is painful or sets you back. however, rest is NEVER a good rehab. every day of prolonged rest means atrophy for your muscles.
use this time to work on your mobility and strength, especially your posterior chain. work on dynamic stretches, foam/ball rolling, then progress to split-leg squats (lunges with weight), and eventually barbell squats (start with light weight and add a couple of pounds every time), deadlifts (try to do these as early as possible. start light, add weight every time). deadlifts are really one of the most important exercises for all athletes and especially hockey players. bench (or overhead press) and pullups are also your friends, even if some old timers will tell you otherwise. look into kettlebells when you are ready to add explosive movements.
one other thing to note, pay attention to your form on all exercises. watch youtube videos, read blogs and books by authors you trust. PM if you need ideas.
protein advice is good as you need to get enough of it (1-1.5g per lb of body weight), but it won't retain muscle by itself. you will also need progressive load. besides that, take plenty of fish oil and vitamin d. if your bones are taking a little longer to heal, drink lots of milk. don't be afraid to add 20 lbs while you are sidelined. it will take effort to lose that extra weight (cut the calories, increase work capacity), but that's doable and much-much safer than coming back to the game at only a fraction of your former strength.
good luck on your recovery.
