"Villanueva didn't do anything to get taken out of a rotation," Cubs manager Dale Sveum said Friday. "It's more about getting a young kid here who we want to see pitch and finish out the season in the rotation."
Villanueva has seen Arrieta pitch, and he could understand the change.
"If we can have a guy in here who can be a contributor in that role -- and I think he can be, because he has great stuff -- then we have to see what it is," Villanueva said. "You can't have six guys or seven [in the rotation]. I wish we could. I'm not super excited to not be starting, because I wanted to be starting. But if this is where I can help, I'll gladly do it and accept my assignment. I always have."
The Cubs could use an experienced arm in the bullpen with the loss of Matt Guerrier, who underwent surgery on his right elbow Friday and is done for the season.
Villanueva began the year in the rotation, then switched to the bullpen when Matt Garza returned from the disabled list. In 15 starts, Villanueva was 1-7 with a 4.50 ERA, and he has a 3.66 ERA in 17 relief appearances.
"I felt I did a good job and I gave the team a chance to win," Villanueva said. "I'm grateful that I got the opportunity to start. If it's the Cubs or another team that sees me doing that in the future again, then I'm ready for it. Right now, the Cubs need me to be in the bullpen, and that's where I'll be and that's where I'll do my best."
Villanueva is one start shy of his single-season career high for starts (16), set last year with the Blue Jays. But he also pitched in 22 games in relief for Toronto. In his career, Villanueva has started 71 out of 333 games. He admits that being versatile can be "a pain in the butt," but knows it's kept him in the big leagues.
"Now I'm at a stage in my career, I want my motivation to be more than just being in the big leagues. I want it to be winning and a winning atmosphere," he said. "If bringing Arrieta here and having [Chris] Rusin have more seasoning behind him to help for next year, it shows me that next year if I'm in the bullpen and we're popping champagne here, I'll have no worries in the world."
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.