"You've got to be ready to pitch at any time, like we saw yesterday with Rusin -- whether it's one day or a couple weeks or the whole season," Parker said. "I'm glad I'm back up here and I want to contribute any way I can."
Parker appeared in 49 games in 2013 with the Cubs and compiled a 2.72 ERA and was a candidate for the bullpen on Opening Day, but struggled in Spring Training and opened at Iowa.
"This offseason, I wanted to come in ready to go and didn't really pitch the way I wanted to this spring," Parker said. "My arm felt good, my body felt good, I just wasn't getting it done."
The Cubs are trying to fill in for Jose Veras, who will be used in a different role after his struggles in his first four games. Parker is the career saves leader at Iowa, and knows how hard it is to get the last three outs.
"It's an unbelievably hard role, especially in the big leagues with the crowd involved and the umpires are a little bit tighter and the quality of the hitters is way better," Parker said. "It's the hardest job for a pitcher to get those last three outs. To just be able to come in and get outs is my thing, whether it's the ninth or the sixth."
Renteria said he'll use Parker, Pedro Strop, Hector Rondon or Justin Grimm in save situations.
"They give me various options," Renteria said. "You still have to put them in situations where they feel comfortable."
The Cubs have seen two pitchers -- Strop and Rondon -- each record a save within the first 11 games of the season. Last April, the Cubs had three different pitchers record a save within the month of April for the first time since the save became an official MLB statistic in 1969.