Losing muscle isn't the primary concern if you are obese.
The body is so loaded with fat, that it is extremely difficult to do lose
muscle first. And you would be surprised about the muscle mass of many large people, lying underneath the layers too.
Obviously, doing some weight training is a good idea just because.
But if you have to trade in calorie burning cardio then it is probably not
a wise investment. Once or twice per week is enough if you are obese.