You grow while you're resting. That means if you play football every day you will not gain as much as you could, because your body doesn't have the time to build new muscles. I would recommend a workout routine with 2 days of training and one day off. But I don't know how many times you have to train on the field. It is very important that you have two days a week where you don't do anything physical.
Stress is a major muscle eater, so stay away from stress.
Take a nap during the day, since this will increase your growth hormone release. Keep your workouts under 1 hour, more than that you are really wasting your time in the gym. Your testosterone level will be so low that you don't get anything out of your workout. Keep your rest in between the sets under 2 minutes, try to keep them by one. Always warm up before you train with 5 min bike riding, since an athlete can not afford to get injured.