Because of the unique Opening Series in Australia, the D-backs were able to carry a 28-man roster, with three of the spots being starting pitchers who remained in Arizona. Without the need to carry more than two starting pitchers, the D-backs will play this series with 10 relievers.
After a strong start to the spring, Bradley has struggled in his past two starts, including Friday night against Team Australia.
"His first two were outstanding," Towers said of Bradley. "Last couple looked like he struggled a little bit with his fastball command, falling behind and wasn't landing his breaking ball as much as he needs to. The first two, that's all he did was pound the strike zone."
Bradley is likely to get one more start before the stateside opener on March 31, and the team will work to get Delgado stretched out next week.
There is only one rotation spot open, but that could change if veteran Bronson Arroyo has a setback in his recovery from a bulging disc.
Steve Gilbert is a reporter for MLB.com. Read his blog, Inside the D-backs, and follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.