BOSTON (CBS) — Tyler Thornburg has yet to throw a pitch for the Red Sox, but Boston’s December swap for the reliever got a little more expensive for the team on Monday.

The Red Sox completed the trade by sending Yeison Coco, an 18-year-old middle infielder, to the Brewers as the “player to be named later” in the deal that already included third baseman Travis Shaw going to Milwaukee.

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Coco made his professional debut last season for the Dominican Summer League Red Sox 2, batting .308 (80-for-260) with 41 runs, five doubles, nine triples, one home run, 26 runs batted in, and 12 stolen bases. He originally signed by the Red Sox in 2015, and entered the 2017 season ranked by Baseball America as the Red Sox’ No. 25 prospect.

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In addition to Shaw, who has hit .292 with 10 homers and 40 RBIs in 50 games for Milwaukee this season, the Red Sox previously sent shortstop prospect Mauricio Dubon and Single-A pitcher Josh Pennington to the Brewers as part of the trade.

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Thornburg, 28, has been on the shelf for Boston since Spring Training as he continues to recover from a right shoulder impingement.