McGree stands as Charlotte’s second-ever signing after penning a deal in October 2020, and departs before the MLS expansion side plays a game.
“We knew Riley was being tracked by a lot of clubs across Europe after his successful spell at Birmingham, and we finally fielded an offer that was too good to turn down,” sporting director Zoran Krneta said in a release.
“To sell a player for profit that has never played a game for your club is a testament to our incredible scouting department who identified Riley as a player with a bright future.
“We will invest this transfer fee back into our inaugural roster as we continue to build towards the start of 2022. Everyone at the club wishes Riley the best of luck at Middlesbrough and throughout the rest of his career.”
The 23-year-old Australian international spent the last year-and-a-half on loan at Birmingham City and recorded 30 appearances at the second-division side.
McGree now joins Championship side Middlesbrough as they battle to gain promotion to the English Premier League. They currently sit seventh in the standings.
The player was previously linked with a move to Scottish Premiership powerhouse Celtic FC before transferring to Middlesbrough.
Without McGree, Charlotte still have Jordy Alcivar, Alan Franco and Sergio Ruiz as key midfielders. They also added Ben Bender to the roster after selecting the player as the Number 1 overall in last week’s 2022 Major League Soccer SuperDraft.
Riley McGree became the latest Major League Soccer player to transfer to Europe, after Orlando City forward Daryl Dike secured his move to Championship side West Bromwich Albion, FC Dallas agreed to a deal with FC Augsburg for Ricardo Pepi and Toronto FC sent Richie Laryea to Nottingham Forest.