The Union will sell centerback Mark McKenzie to Belgian club KRC Genk, multiple sources tell The Inquirer, in a deal that starts at $6 million and should go higher.

News of the deal broke Monday night when two Belgian newspapers, Het Belang van Limburg and Nieuwsblad, said the deal was close to done. The Union have kept quiet, knowing how many suitors McKenzie had. Scotland’s Celtic was the loudest, reportedly bidding $3-4 million. There was also reported interest from English and German teams.

A source confirmed a report on Major League Soccer’s website that the transfer fee will start at around $6 million, then add performance incentives. There’s also a sell-on fee that would give the Union a piece of a future sale. The values of the incentives and sell-on fee aren’t known yet.

McKenzie, 21, moves on after three seasons in MLS. Born in the Bronx, N.Y., and raised in Newark, Del., he attended the Union’s youth academy high school in Wayne, then spent one year of college at Wake Forest. He turned pro at the start of 2018, and scouts were already raving about him. They were quickly proven right: Of the 59 games McKenzie played here, he played every minute in 55 of them.

His stock with the U.S. national team also rose fast. In May 2019, he captained the Americans at the Under-20 World Cup, and nine months later, he earned his first senior cap. On Dec. 9, he earned his second, playing alongside former Union teammate Brenden Aaronson.

McKenzie grew off the field as much as he did on it. He was a leader of the Union’s anti-racism campaign this year, developing a strong voice on camera and on social media.

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Genk is in second place in Belgium’s first division, a league that many Americans call home. The biggest names are goalkeeper Ethan Horvath, who plays for first-place Club Brugge, and centerback Matt Miazga, who’s at traditional power Anderlecht.

Genk won the Belgian league in 2019 and reached European tournaments seven times in the 2010s. Last season, the club played in the Champions League group stage, but hit a rough patch domestically and finished seventh. So it’s not in Europe right now, but it’s on track to return next year.

Just as importantly, Genk has a significant track record of developing future stars. Famous alumni include Manchester City playmaker Kevin De Bruyne, Real Madrid goalkeeper Thibaut Courtois, and Atletico Madrid midfielder Yannick Carrasco. All three men played on the Belgian national team that finished third at the 2018 World Cup and is now No. 1 in FIFA’s global ranking.

Jamaican national team winger Leon Bailey played at Genk before making a $15 million move to Germany’s Bayer Leverkusen in 2017. Toronto FC midfielder Alejandro Pozuelo, this year’s MLS MVP, spent four years at Genk before joining the Reds in March 2019 for $11 million.

So McKenzie’s deal resembles what the Union got for Aaronson from Red Bull Salzburg, in terms of both money and the buying club. It makes sense for the Union to sell young players to European teams that will develop them for bigger suitors. When those deals come, the sell-on fees kick in and the Union get another sizable check.

» READ MORE: Union sell Brenden Aaronson to Red Bull Salzburg for $6 million, launching the Medford native to Europe’s soccer spotlight

If McKenzie does well at Genk, the suitors will notice, because they’re already watching the club closely. In the last two years, Genk has made five sales for eight-figure transfer fees, three to English Premier League clubs and two to Italian Serie A stalwart Atalanta.

The biggest deal was Norwegian central midfielder Sander Berge to Sheffield United for $28.8 million. Belgian winger Leandro Trossard went to Brighton & Hove Albion for $22.9 million, and Tanzanian striker Mbwana Samatta went to Aston Villa for $11 million. Atalanta bought Ukrainian midfielder Ruslan Malinovskyi for $15.3 million, and just a few days ago bought Danish right back Joakim Maehle for $12.1 million.

Add all that money up and you get a club with a track record of winning games, developing players, and getting the rest of Europe’s attention. It’s the right formula for McKenzie, and for the Union.

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