The Reds acquired Holmberg from Arizona in a three-way offseason trade that sent catcher Ryan Hanigan to Tampa Bay.
Ace Johnny Cueto is expected to start Game 1 on Tuesday vs. Chicago.
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, and follow him on Twitter @m_sheldon. Manny Randhawa is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.