Two key tenets of successful team building in baseball: First, deal from strength, and second, take advantage when the market overvalues your assets. Brian Cashman may find himself in the unusual position of meeting both conditions for making a trade when it comes to his center fielder, Melky Cabrera.

Cabrera is a bundle of contradictions: a functional defensive center fielder with a great arm but unexceptional range; a mostly inoffensive hitter whose hot streaks are outnumbered by deep slumps; a young player with a better future in front of him, but not a great future, and a switch-hitter who has almost no offensive value against left-handed pitchers. Taken together, these competing facets make Cabrera a difficult player to get a fix on. If you saw him at midsummer last year, when he batted .325 AVG/.375 SLG/.482 OBP from June through August, or this April, when he hit .299/.370/.494 with five home runs, you could have been forgiven for thinking that he had taken a dramatic step forward and was now on his way to becoming a two-way impact player and a 10-year All-Star. If you saw him last April (.200/.238/.213) or September (.180/.236/.220), or this season over the last eight weeks (.231/.280/.308 in 47 games), making outs while attempting to slide into first base, you might be wondering why he’s not been sent to Double A for a refresher course in basic baseball 101.

Unfortunately, the latter Cabrera appears for more often than the former. Fortunately for the Yankees, talent evaluators tend to put less emphasis on transient slumps and more on ground-floor values like “proven major leaguer.” There are many teams hoping to play into October, and a few who won’t, who could use the small assurance that Cabrera would provide. The Yankees, who will likely need more pitching to continue their current run of strong showings against weaker ball clubs, not to mention survive the first round of the playoffs should they actually pull off their third amazing return from the dead in the last four seasons, might be able to leverage Cabrera as part of a package for the extra arm they need.

The reason the Yankees can deal their starting center fielder for need without opening up another hole is the performance of prospect Brett Gardner at Triple-A Scranton. The speedy center fielder is currently batting .292/.408/.436 with 10 doubles, nine triples, three home runs, and 52 walks in 73 games. He has also stolen 29 bases in 37 attempts. Gardner, 24, will not be an impact player in the major leagues. However, given his patience, a .275 batting average, and his ability to run balls down with his speed, he should be at least as productive as Cabrera and provide a better on-base threat at the bottom of the order, creating more opportunities for Johnny Damon, Derek Jeter, and the top of the lineup.

Additionally, his baserunning ability would give the Yankees an added touch of speed that is sorely missing from this year’s roster. Perhaps Gardner would not put a charge into the Yankees the way Jacoby Ellsbury did with the Red Sox last fall, but the general impact would be the same, the injection of some athleticism into what has traditionally been a more plodding roster. Altogether, dealing Cabrera would be a win-win for the Yankees, allowing them to improve their club from within while also allowing them to bring in more help from without.

Brian Cashman is not one to make deals easily, and he has some past examples of catching lightning in a bottle, with journeymen pitchers such as Shawn Chacon and Aaron Small, as additional inhibitors to trading — why buy what you can make? But as Casey Stengel once said, “Sometimes it doesn’t always work.” These transformations are not dependable, and in any case, to paraphrase Billy Beane, that [expletive] doesn’t work in the playoffs. Postseason success is highly dependent on being able to run out the swing-and-miss pitchers who can keep the Albert Pujols types contained at home plate. As we have seen repeatedly with Chien-Ming Wang, by the time you reach October, the teams with Tony Pena Jr. in the lineup have gone home, replaced by teams whose worst hitter might be, say, Julio Lugo. When those teams put the ball in play, it tends to do damage as often as it dribbles weakly to the shortstop. Dan Giese, Darrell Rasner, even Mike Mussina, this means you.

None of this is to say that the Yankees can’t continue to try with their farm-raised options or even (choke) Sidney Ponson, but when a team can make a deal for an established hurler who could take an underdog and propel it forward, and do so with a player who has been made redundant by his own poor play and the presence of a superior prospect, such a move is a no-brainer. Those “Got Melky?” T-shirts will look great in Mariners colors, but a last pennant for the old Yankee Stadium would look even better.

Mr. Goldman writes the Pinstriped Bible for yesnetwork.com and is the author of “Forging Genius,” a biography of Casey Stengel.