Cliff Lee has not yet decided whether to accept one of the Yankees' offers for his services. Despite the guaranteed birthday pizza parties, Lee is still vacillating. He could simply be taking his time, but the delay suggests he may be seriously considering an option which pays him less but keeps him out of New York. After all, if money was the only consideration he'd simply pick the biggest contract and that would be that.
If the Yanks wait for Lee to decide before seriously getting involved in Greinke conversations, the Royals will be in a position to dictate a deal much more on their terms. It is possible that the Yankees pursuit of Russell Martin is evidence of an attempt to free up Jesus Montero for a potential trade. But a Greinke deal shouldn't be plan b. This should probably be a 'whatever comes first' situation.
If you're on the verge of a trade for Greinke, then Lee can't waste anymore of our time. You might even pull the Lee offer off the table. People don't like giving up a lot of prospects, and it will take a lot, but Greinke has the goods (granted, whether he can handle NY is a big question; but hey, if he can't, he's a hell of a trade chip). The Yanks have a lot of pitching talent in the minors; coupled with some of our position prospects, we may have the ability to pull off a trade with the Royals. Perhaps it's worth not waiting until we're in a position of weakness to begin serious conversations about Greinke.