That's right decision of course. If Rafa is not ready, then he should not play. Starting the season at clay tournaments might be actually a good idea.
Btw, Fed did not have mono at AO. Ancic had mono, Soderling had mono, Fed never did. He just made up this story because him never being injured or sick makes everyone suspicious. I guess he believes he may be jinxed too. Or Mirka does. And we know who rules in that family.