The Mets acquired Carreno from the Pirates on Tuesday in exchange for left-hander Josh Walker.
Carreno, who turned 18 in June, is a left-handed starter who is in his second tour of the Dominican Summer League. He has a 3.74 ERA, 1.29 WHIP and 36 strikeouts in 21.2 innings this season, although his 17 walks illustrate the work he needs to do with his control.