The Diamondbacks will return Rule 5 choice Marcos Mateo to the Cubs, reports Paul Sullivan of the Chicago Tribune (via Twitter). The right-handed reliever was the eighth player chosen in this year's draft, though he was selected from the 15th slot.
Since seeing time in the bigs over 2010-11, Mateo missed all of 2012 and threw at Triple-A last year. In 31 innings, he posted a sparkling 1.74 ERA, with 8.7 K/9 against 3.8 BB/9. Across his previous 44 2/3 MLB innings, Mateo notche only a 5.04 ERA but for every nine innings did manage to strike out 10.3 while surrendering only 3.8 free passes.
As with most Rule 5 choices, Mateo would have struggled to stick on Arizona's roster for the year. That was especially so given the number of additions and commitments the team made to the pen made over the offseason. As MLBTR's Tim Dierkes has noted, Mateo was among the NL West players who are out of options. As a result, Arizona had little reason to work out a trade to retain Mateo's rights, since it could not hold onto him in the minors without passing him through waivers.