The Cubs claimed right-hander Ryan Cook off waivers from the Red Sox on Friday, and the team's 40-man roster now stands at 30 players.
Cook, 28, is 13-12 with 17 saves and a 3.43 ERA in 217 Major League relief appearances over parts of five seasons with the D-backs (2011), A's (2012-15) and Red Sox (2015).
He has struck out 210 batters in 207 innings while walking 89 and allowing just 13 home runs.
Cook spent most of the 2015 season in the Minors with Oakland's Triple-A Nashville affiliate and Boston's Triple-A Pawtucket affiliate, going 4-1 with nine saves and a 3.16 ERA in 37 outings.
He made nine Major League relief appearances in 2015, going 0-2 with an 18.69 ERA in 8 2/3 innings.
Joey Nowak is a reporter for MLB.com. Follow him on Twitter at @joeynowak. This story was not subject to the approval of Major League Baseball or its clubs.