The FC Dallas star is on the move to Turkey, but he could return to the MLS club if Trabzonspor doesn't pay another $2 million in January.

FC Dallas leads the MLS Supporters' Shield race, has advanced to the U.S. Open Cup semifinals and kicks off its 2016-17 CONCACAF Champions League campaign next week. Yet it’s on the verge of finalizing the transfer of Fabián Castillo, a Designated Player who’s the club’s leading active goal scorer.

Castillo, 24, is on his way to Turkey’s Trabzonspor, which is eager to improve on last season’s disappointing 12th-place finish in the Süper Lig. The deal could be finalized on Tuesday and is not a straightforward transfer, SI.com understands. Trabzonspor will pay around $2 million to secure Castillo’s services for the next six months. It then must pay another $2 million before or during January 2017 to seal a permanent move. If that second check isn’t written, Castillo’s rights would remain with Dallas. The transaction is a transfer at heart–that's the intention and understanding on both sides–but in practice it's a loan until the entire fee is paid.

FCD will keep two-thirds of the transfer fee, according to MLS rules. The rest goes into the league’s account.

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Castillo is one of FCD’s three DPs. According to figures released by the MLS Players Union, the Colombian earns only $170,750 per season. His total likely is significantly higher in actuality, and he’s almost surely in store for a significant raise in Turkey. Castillo is thought to be excited by the prospect of playing in Europe, and he didn’t travel for Saturday’s top-of-the-table clash at the Colorado Rapids as details of the loan/transfer were ironed out.

Castillo’s impending move was reported first by Goal.com.

Castillo has been a massive part of FCD’s resurgence under coach Oscar Pareja, who brought the winger to Texas back in 2011. At that point, Pareja was an assistant coach and ran the club’s soon-to-be-vaunted academy. He acquired Castillo through connections at Deportivo Cali, where Castillo was playing and where Pareja spent three years in the 1990s. Castillo lived with Pareja and his family while getting adjusted. He finally blossomed in 2014, netting 14 goals in all competitions as Pareja, who’d moved to the Rapids, returned to Dallas as head coach.

Castillo made his debut with the Colombian national team last year and this season has six goals, five in MLS play and one in the 91st minute of last week’s Open Cup quarterfinal in Houston. He also has five assists, including one on this audacious rabona vs. the Chicago Fire on July 16:

There’s no like-for-like replacement on FCD’s current roster—Castillo’s combination of speed and technique is tough to find—but Pareja rotates players in and out and has some depth with which to work.

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In Argentine Mauro Díaz, FCD boasts one of the league’s top playmakers. Michael Barrios, Tesho Akindele, Maxi Urruti each has at least five league goals. At Dallas there always are youngsters coming through the pipeline, and Pareja will have the opportunity to offer younger players like Coy Craft more minutes or experiment with Kellyn Acosta, Carlos Lizarazo, Ryan Hollingshead, Atiba Harris, Mauro Rosales and others.

Plus, the club now has an extra $1.33 million to play with this summer. FCD also may be due a portion of a subsequent transfer fee paid for Castillo to Trabzonspor, depending on the terms of the deal finalized this week.

Trabzonspor kicks off the 2016-17 season on Aug. 20 against Kasimpasa.