"We're a little banged up with our bench right now," Reds manager Bryan Price said. "We have some guys that are a little beat up. They can play, but there are some limitations to what they can do. An extra bench player, at this point in time, is imperative. It's nice to have a left-handed bat on the bench."
One of the sore players is switch-hitting backup catcher Ramon Cabrera, who has been dealing with a left middle finger injury from a foul ball. Cabrera played through the injury on Friday.
"He's a gamer. He sucked it up yesterday," Price said. "He got another foul ball in the same spot."
Although Cabrera or fellow switch-hitting catcher Tucker Barnhart -- when he's not starting -- can be lefty options on the bench, Price can use Waldrop without burning his backup catcher.
"I don't want Wally here for a month pinch-hitting two or three times a week. He needs to be playing," Price said. "I think he's capable of contributing off of the bench, at least in a short spurt."
Diaz had a 15.75 ERA in five games since his May 22 promotion. He last pitched on Tuesday at Colorado and allowed five earned runs on four walks and two hits, including a homer, over two-thirds of an inning.
• For the first time since a late April setback during his rehab assignment, Reds pitcher Homer Bailey threw from a mound in the bullpen. Bailey reported feeling good during the session.
"He looked really good. He looked terrific," Price said. "We had to kind of peel everything back a ways and shut him down [in April]. His arm is in good shape. He's gone through all the long-toss progressions, flat ground work and now the first day of bullpen progressions, which will increase in total pitch number before we have him throw live batting practice or a simulated game. And then back into regular game activity building his pitch limit to where he can help us."
• Like the rest of the world, members of the Reds were saddened by the overnight passing of boxing legend and humanitarian Muhammad Ali at the age of 74. Second baseman Brandon Phillips met Ali when he was in Cincinnati for the 2009 Civil Rights Game at Great American Ball Park.
"He's the greatest of all time," Phillips said. "You think about him, he spoke his mind regardless. He really showed up. He did his thing. He proved it. All I can say is rest in peace easy."
The Reds observed a moment of silence for Ali before Saturday's game vs. the Nationals.
Mark Sheldon has covered the Reds for MLB.com since 2006, and previously covered the Twins from 2001-05. Read his blog, Mark My Word, follow him on Twitter @m_sheldon and Facebook and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.