Capped twice by Denmark, the Ugandan-born 21-year-old came through Midtjylland's youth system and his efforts to help his side secure the 2015 Danish league title attracted the interest of a slew of top European clubs.
"He has earned it," Midtjylland sporting director Claus Steinlein said in a statement. "He has both a huge talent and an enormous will, desire and hunger to be a football player."
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No financial details of the transfer were announced and Sisto will join up with Celta Vigo, who finished sixth last year, ahead of their opening La Liga fixture against Leganes on Aug. 22.
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