NEW YORK — For the first time in league history, Major League Soccer has implemented a rule that permits loans between its clubs, and it's quietly been in place since the beginning of the 2013 season.

The existence of the trade mechanism since the very start of the league in 1996 meant that loans were initially deemed unnecessary within the MLS structure.

But times have changed. With the proliferation of MLS academies, the expansion of rosters and the increase in squad depth — especially the signing of more accomplished and talented young players — means there's more flexibility. And now, more opportunities for those young players.

READ: Recap of MLS players out on loan to lower-division teams

"The loan rule is meant to get young guys moving more within the league, especially if they're not playing for their team," explains MLS vice president of player relations and competition Lino DiCuollo. "Teams can now execute trades involving loans, without having to permanently give up a player's rights."

Your team has a crisis at left back? Now it can arrange for a trade involving the loan of a young left back who is riding the pine on another MLS team. The terms of that trade, which can include other considerations exchanging hands in addition to the loan, are negotiated between the teams and approved by the league.

SEE: Team-by-team transactions in 2013

But there are some basic guidelines that govern loans, as explained by DiCuollo:

I) Only players 24 years of age or younger are eligible for loans;

II) Loans must be executed within the primary transfer window of a given MLS season (Feb. 12-May 6 in 2013);

III) All loans run through the end of the MLS season (player reverts to his original club only after MLS Cup);

IV) Roster slot and budget considerations surrounding the loan are subject to negotiation between the two clubs;

V) There are no limits on the number of loans involving any one team (incoming or outgoing loans).

We'll see which player makes history and becomes the first intra-league loanee.

The clock is ticking, however. If it's going to happen, there are only 18 more days left in the primary transfer window closes.