Bodybuilding injury question?

I've been working out for 3 years now and i can see my muscle gains slowing down. i've messed up my knee during a rugby match last week and i need surgery. the recovery could take months... during my recovery theres no doubt that i will loose muscle... when i am cleared by my doctor to exercise again i will be skinny as hell, if i start working out again after my recovery will i gain muscle as fast as i did when i first started off working out? aka newbie gainz?