When our cat was so sick with those drainage tubes, she would only accept human tuna in water. Mostly the water satisfied her.
She really lived off her fat--she was big like Chewy.

I left little bits of tuna in the water.. so she would get the protein. But she wouldn't take solids much.

My 21 yr old cat gets a shredded real cooked shrimp daily. After starting her on this, is when she became the longevity cat. Our vet expected her death 4 yrs ago!.

Some cats like chicken... you could mash chicken up and liquify it in water.

For a short time, the taurine issue most likely would not be serious. But some cat food eventually is needed because cats need taurine (it is in commercial foods). Taurine comes in capsules for people and you could use this eventually.

If he is sluggish (that narcotic pain shot is very sedating) keep his bed area, water/food and litter box all in one spot where he can get at it with little effort on his part.

Is he purring alot? Purring alot means pain, and sometimes helps them heal.

I was just a kid when this happened to our poor cat. We had just moved into this house
(a family home) and could let our cats outside for the first time. Pepper got attacked on our porch. I felt so bad because we didn't know it happened. The surgery was over $300 back in the 70's and I just indulged her when she came home. Back then there was no Science Diet, fixey pain shots, or fixey antibiotics. I guess it was a miracle she survived.
But I was like a nurse 24/7 for a month when she came home!