My Cat has a Broken Pelvis

[simpcas@freenetname.co.uk]

Hi
Hope someone can help.
My cat was diagnosed a couple of weeks ago with a broken pelvis. He seems to be on the mend as he is walking better, and tries now to fight me when I'm giving him his painkiller.
Our problem is that he has gone from being a real 'muncher' to hardly eating anything at all. He has a few nuts (we use Hills Science Plan) occasionally and some water, but won't eat his tinned cat foot which he used to love.
The Veterinarian doesn't think there is any internal damage apart from the pelvis, and he's going outside to urinate/defecate as normal.
Could there be some underlying mental problem which is putting him off his food?
Does anyone know how we can increase his appetite & desire to eat?
Thanks