Britton was claimed off waivers from the Red Sox in early February. In nine Cactus League games, Britton gave up three earned runs on eight hits and four walks over 8 1/3 innings.
With the open spot on the 40-man, the Cubs could add infielder Jonathan Herrera, who was a non-roster invitee this spring.
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.