So I fucked up my right shoulder/arm pretty good (rotator cuff injury, bicep tendonitis) and I've been told by my physiotherapist not to do any weight-lifting/arm strength exercises (other than the ones she recommends for recovery) for the next little while. However, I'm worried about losing some/most/all of the muscle I have put on over the last 6 months or so.

So my questions are, how quickly will I begin to lose muscle and is there any way to prevent it from happening or to slow it? I'm still doing intense cardio, so it's not like I'm just sitting on my ass and packing on the fat.