Nathan signed with the Cubs on May 17 and was placed on the 60-day D.L. while he continued to recover from Tommy John surgery that took place in April, 2015. He posted a 3.86 ERA (4 ER/9.1 IP) with an 0-1 record, five walks and nine strikeouts spanning 11 relief appearances during injury rehabilitation assignments with Double-A Tennessee and Triple-A Iowa from June 23-July 20.
Nathan is a six-time All-Star who has earned 377 saves, eighth most in major league history, during his 15 major league seasons with San Francisco (1999-2000, 2002-03), Minnesota (2004-09, 2011), Texas (2012-13) and Detroit (2014-15). He surpassed 30 saves in nine of 10 seasons from 2004-14, including four seasons with more than 40 saves, and recorded 35 saves with Detroit in 2014, his last full big league campaign. He made only one appearance with the Tigers last year before enduring his elbow injury in April and missing the rest of the season.
Overall, the righthander is 62-34 with 377 saves and a 2.89 ERA (294 ER/917.0 IP) in 777 major league appearances, all but 29 in relief.
Warren, 28, is 3-2 with a 5.91 ERA (23 ER/35.0 IP) in 29 games, including one start, for Chicago this season. He has no record and a 4.15 ERA (4 ER/8.2 IP) in two starts with Iowa this year.