Cubs activate Joe Nathan, add to bullpen

MILWAUKEE -- The Chicago Cubs have activated veteran reliever Joe Nathan, whowill be available out of the bullpen for Sunday's game.

The 41-year-old Nathan ranks eighth all-time in big league saves with 377. He joins a first-place club that has struggled with inconsistent bullpen work for much of the season. Nathan's immediate role has not been defined, but he is not expected to supplant Cubs closer Hector Rondon.

Nathan underwent Tommy John surgery in April 2015 and hasn't pitched in the majors since. He last appeared in a big-league game on April 6, 2015, with the Detroit Tigers.

He signed with the Cubs on May 17 and just completed a 30-day rehab assignment with Iowa. He said he is mentally ready to go from rehab mode to the beat of a pennant race.

"I treated [rehab] kind of as my spring training, so this is going to be like Opening Day for me," Nathan said. "It's definitely going to be a jump in my nerves, but I'm expecting that. I will try to keep myself calm like I have for a number of years on Opening Day."

The Cubs optioned righty swingman Adam Warren to Triple-A Iowa to open a spot on the 25-man roster.