Red Sox manager John Farrell confirmed the news after his team’s 8-4 win over the Tampa Bay Rays on Friday night at Tropicana Field.
The Red Sox’s GCL team will square off against the Yankees’ affiliate in a three-game finals series, which takes place in Fort Myers, Fla.
The 27-year-old from Cuba signed a seven-year, $72.5 million free-agent contract earlier this month.
Castillo played five seasons in Cuba’s Serie Nacional, posting a .319/.383/.516 slash line with 51 home runs in 360 games.