Are you sure he/she is living there or just passing through? Maybe was chased under there by local cat,dog or fox? I’d give it a day or two and see if it’s still there as there are not prone to living close to us to be honest.
If it’s still there I’d send it a bill for rental accomodation 😀
Or just give a prod with a broom (give it a escape route don’t have the garden full of every one just you go on your own and let it run in the opposite direction and out from the decking) if wild it will be gone if it stays it’s either a lost pet or injured and may make a decent stew*
* Depending or said injury.