The Secondary Transfer Window is open, and with it, the trade market. As MLS general managers get busy looking for ways to improve their respective teams, they're constantly assessing who holds the best trade chips in the league, and how they can best leverage their own into a season-altering deal.

Quality is just one of the variables weighed. In picking out the plums among players that could conceivably be whisked out of their current homes, other factors enter, such as the going rate for allocation exchanges, the volume of competitive bids and the size of the hole potentially being filled.

That latter reason is why the New York City FC attack duo of Tommy McNamara and Rodney Wallace narrowly missed out on the top five; NYC don't require any major transactions, meaning the veteran duo likely have more value staying in their squad for a title run. Other honorable mentions are Dairon Asprilla, Jahmir Hyka, Clint Irwin, Russell Teibert and Victor Ulloa.

No. 5: Zac MacMath

Were more clubs searching for a potential starter, Colorado Rapids’ backup 'keeper Zac MacMath could have ranked higher on the list. Colorado, conversely, should be eager to make any deal that can improve the side.

MacMath hasn't been "the man" for a full season since 2014, but he's gone 12-12-7 with a 1.16 goals-against average for Colorado (numbers that top those of Rapids star Tim Howard, actually). The 26-year-old is a good shot-stopper who also distributes very well.

Who should consider inquiring: As things stand around the league, San Jose should be the first team in line any time a quality netminder might be had in a swap.

No. 4: Russell Canouse

Russell Canouse (in black) | USA Today Sports Images

Seeing as how D.C. United midfielder Russell Canouse is just back from a knee injury, one could just as easily tab Jared Jeffrey or Ulises Segura here. Canouse would draw the most in return, so we'll stick with him.

The Black-and-Red definitely have a central midfield logjam, and the Pennsylvania native may be the most tradeable one in the bunch. While the 23-year-old can surely improve in the ball security department, any team desperate for a gatekeeper who can shut down rushes would be happy to have him.

Who should consider inquiring: Several teams are either hurting at the defensive midfield position now or nearing time to find the successor to an aging standout. The injury struggles of Juan David Cabezas are the main reason Houston stand below the Western Conference playoff line. That defense sorely needs protection.

No. 3: Alex Crognale

Alex Crognale (right) | USA Today Sports Images

Columbus Crew SC defender Alex Crognale is currently marshaling the best defense in the USL's Western Conference on loan to Orange County. Homegrown product Crognale is there because Jonathan Mensah rediscovered his mojo and Lalas Abubukar came of age.

The 23-year-old was a bit of a time-of-need revelation for Columbus last season, and they only leak one goal per game in which he plays at least an hour. The defender, who rings up over seven clearances per 90 MLS minutes, could be best served as a fire extinguisher in a team that spends time in a three-man backline setup (paying attention, Colorado and Minnesota?).

Who should consider inquiring: How long ya got? There are 8-to-10 clubs who might be tempted. But most eager to hop on WhatsApp with Gregg Berhalter? It would certainly be fine timing for D.C. United to pull the trigger on a playoff drive deal like this, for sure.

No. 2: Juan Agudelo

New England Revolution attacker Juan Agudelo remains as exciting with potential as he is confounding. Agudelo has yet to score more than eight times or start more than 21 games in a single MLS season, but if he ever puts it all together ... look out league.

That may well not happen under New England boss Brad Friedel; not only has the new coach moved him further from goal, but Saturday's start was just the fifth in 15 appearances for Agudelo this term. And, gosh, you'd think that the quick-footed US international would feast atop the Gillette Stadium crew's press... (shrug).

Who should consider inquiring: It's not crazy to imagine Agudelo "pulling a Zardes" if teamed up with wily string-puller Albert Rusnak and his sidekick posse of crossers over at striker-starved Real Salt Lake.

No. 1: Joao Plata

Speaking of RSL, they may just hold the most tempting chip of the summer. David Gass stated on Monday's ExtraTime Radio show that some enterprising GM should get on the horn to discuss Joao Plata, and it's a notion worth a second.

The diminutive Ecuadorian has chalked up 5 goals and 2 helpers in just 688 minutes this season, and yet can't nail down a starting place. The 26-year-old is quality, but not the specific type of attacker Mike Petke's team really needs.

Who should consider inquiring: In his last 139 games across all competitions, Plata has bagged 46 goals to go with 31 assists. Not to sound indelicate, but Columbus would punch a unicorn in the nose for that kind of production from the wide channels.