My 18 month old boxer has just had to have a cruciate repair.  He had it done on 2nd May.
The op went well but he is very miserable (due to pain) and is off his food and as he has always been lean he now looks skinny.  He will eat bits of his regular food but I was wondering if something such as AG Prestige (seen it recommended on here a few times) for the recouperation period would help bulk him up a bit and provide the extra calories etc.

I am not concerned about him becoming overweight due to a higher density food and minimal/no exercise as this would be well monitored and I think it would be really difficult for him to become a fat dog. 

He will eat chicken wings, eggs treats etc but still not over enthusiastically as he normally would.  Whilst he will eat these I would prefer him to have a balanced diet whilst he is recovering as I am sure that would be no bad thing.

Any suggestions?

Royal Canin Boxer breed specific or Origen both really suit my boxer. 

Is he not on any pain relief still?

TBH, I wouldn't worry about weight yet, let him recover first and get fit again before you fatten him up, too much weight will not help his recovery in my opinion.

Do you have an exercise plan?

Yes sorry he is on pain relief and we took him back to the vets yesterday and they gave him some extra tables to take for 4 days.  He still has the other pain relief to take as well and some antibiotics.

Yep we have an exercise plan but any other ideas are much appreciated

I just wanted to ensure that he was receiving good nutrition so that recovery would be optimal.  At the minute I can easily count all of his ribs and his hips are sticking out too so he doesn't look a pretty picture

I might get a bag of the RC Boxer food and then when he is more recovered switch him back to his other food as he seemed to enjoy it,as does my other dog.  If I get a temporary food would you mix it in with the regular food or just feed it on its own?

I have never seen a dog look so sorry for himself

if you're changing food, then it's best done gradually over a period of days.

My bitch was on about a quarter of her daily rations when recovering from TPLO for cruciate rupture (she was a bit too weighty initially which could have hindered her recovery if left!) she had rimadyl for 2 weeks post op, but has gone on to make an excellent recovery