Parra has not appeared in a game since July 20, but he felt his back ache earlier this week.
"It locked up on me when I warmed up. It was the Sunday day game [vs. the Nationals]," Parra said. "I was getting ready to go into the game."
If the Reds decide to put Parra on the disabled list, it could be backdated to the day after his last appearance. Under the rules however, they could not make the move retroactive if Curtis Partch remains on the roster. It was Partch who came up when Jay Bruce went on the bereavement list after being in Triple-A Louisville for less than 10 days.
Other potential callups like Nick Christiani, Tony Cingrani and Chad Rogers are all injured and on the DL.
Neither manager Bryan Price nor Parra were sure when he could get the green light to get back into a game.
"He's as day to day as they come," Price said. "It always seems like it's a day away from him being a piece of what we're doing. I don't know if he's ready to play. If it seems like it's going to be really a much slower process, we'll have to look at some alternatives with Jay coming back [Friday], just simply because we need to have 25 active, relatively healthy players. As healthy as they can be 100-plus games into the season."
"I just know I felt good today. I'm pleased with the way throwing went," Parra said.
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, and follow him on Twitter @m_sheldon. This story was not subject to the approval of Major League Baseball or its clubs.