As Teresa says, possibly an aged Trametes but to say anything for sure I'd need to be sure of what's on the underside. The upper surface could also fit aged/weathered specimens of Xylobolus illudens and Punctularia strigosozonata. Indeed, the radial and concentric wrinkling inclines me to the latter pair.
@Teresa and @Heino unfortunately I was unable to take a photo of it other than at this angle due to vegetation being in the way and couldn't get in behind it. Thanks for your suggestions.