I always remember watching Andy getting horsed by Stan in a Davis cup match on clay in Switzerland 5 years ago. It will be a different match this time but as we saw in Australia Stan can compete with anyone when he's in the mood.
The Davis Cup match was in 2005 on indoor clay. It's the only (singles) rubber he ever lost. The match 5 years ago was in Rome. Regardless, Andy is yet to win a set against Stan on clay.