Like the other guys said, keep your diet in check, high in protein, and drink plenty of fluids. Don't start to panic if you lose a little weight, because that's probably going to happen to an extent regardless of what you do, but if you work hard to maintain your mass by maintaining an appropriate diet, you shouldn't lose too much in four weeks. And once you start back, it shouldn't take you too long to gain back what you lose in this downtime. Just think of it as a four week vacation!
Also, another supplement you can look into is NAC (N-Acetyl Cysteine). I've read some studies showing it's ability to fight muscle catabolism.
Good luck!