Parker, 28, has posted a 0.77 ERA at Iowa, giving up one earned run in 11 2/3 innings, and has eight saves. He has not walked a batter and struck out 15 in that stretch.
This is Parker's second stint with the Cubs. He was recalled April 13, and made two relief appearances, giving up three runs over 1 2/3 innings.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.