It's unclear at the moment what St. Louis would want back from the Yankees were a deal to happen. The Cardinals' biggest stated need this offseason is a new shortstop, but New York doesn't really have any of those not named Derek Jeter, and even he's questionable given his age and his mostly missed 2013 campaign.
Freese, 30, is a quality player under team control with the Cardinals for another two seasons. Not only is Freese's trade value likely at its peak, but moving him could also make St. Louis' infield situation a little simpler going forward.
As it stands, Matt Carpenter is the club's second baseman, leaving top prospect Kolten Wong without a starting spot in the infield. If Freese is dealt, however, then the RedBirds can move Carpenter to third, where he played almost exclusively in the minors, and let Wong settle in at the keystone for the foreseeable future.
The Yankees, of course, already have a third baseman under contract for $86 million through 2017. You may have even heard of him. However, given Alex Rodriguez's pending suspension and the fact that he's likely to spend a good amount of time at designated hitter when he is playing, the interest in a player like Freese makes sense whether A-Rod (and his $27.5 million in average annual value) are suspended for 2014 or not.
Freese, the 2011 World Series MVP, had a bit of a down year this past season, hitting .262/.340/.381 with just nine home runs in 138 games. While the 100-point drop in OPS is a bit concerning, his numbers are still light years ahead of the production the Bombers got from the hot corner in 2013. New York tried 10 different players at the position and came away with a 633 OPS overall, easily the worst mark in the American League, and that was with Rodriguez contributing a .244/.348/.423 line.