Thanks guys.
Ive given him a check over and theres no sign of any fights and no trace what so ever of any external damage.
It seems to be his tummy that is sore, but Im not certain because it could be his back. But when he was poorly a few months back it has aged him drastically and since then hes been a bit more "aged" when he walks [read stiff sometimes like an old man].
He enjoyed being fussed over and eating, and for a while he was following me from room to room or sat at my feet.
When I took the wheelie bin out, he followed me but at walking pace - normally he'd run back in the house, trying to beat me back in. He sat quietly for a while by me, then he meiowed to be let out the front door (didnt want to use the cat-flap), so he could just be a bit stiff? which is possible if hes been locked in somewhere for practically a week.
I'll keep an eye on him and if he's not any better soon I'll take him for a check-up.
The only other time he went missing was for 3 days a few years ago... and when he came back then, he did look like he'd been in the wars a lil bit.
I bundled him up and took him to the vets within about half an hour of his return, the the vet ran a pile of tests on him (which were all negative) but the tests actually disturbed him far far more than the injuries. He sulked for a week - and found a way to show his disapproval of his visit to the vets. Although I must admit I was very unhappy about the way the tests were conducted because he came back with massive bruising on his throat where they'd shaved his fur and taken samples. I havent been back to the same vets since and registered with one much further away.