A rock or stone would normally be defined under the rules as a loose impediment and therefore no relief would be granted. The player may though remove a loose impediment without penalty provided of course it does not result in the ball moving. Some years ago Tiger got spectators to help move a big rock in the desert that was impeding his line of play.
I guess it is entirely possible that a greenkeeper has put this rock there with the intention of moving it later, in which case it would be classed as ground under repair, of course relief without penalty would then be available, not though sure this is very likely in this case.
