The 30-year-old Guzman has been plagued since before the break with a left thumb contusion, which has had him in and out of Washington's lineup.
Acta indicated before Friday's game against Colorado that Guzman didn't do anything to aggravate the injury, which hurts the most when gripping or swinging a bat.
"He just came to a point where he felt he couldn't go on like that," Acta said.
The Nationals have previously used Guzman as a defensive replacement or pinch-runner when the injury has forced him to sit.
However, Acta said that he'd like to keep Guzman completely out of Friday's game, if possible, to give the thumb more time to fully heal.
Acta added that he thinks the injury will probably be something the Nationals and Guzman will deal with for the rest of the season.
"I'm not anticipating that a couple of days is just going to completely take care of him," Acta said.
Washington had previously run an MRI on the thumb, which revealed what Acta called "soft tissue" damage, but nothing more serious. Further tests on the thumb are expected.
Acta also said that injured right-hander Shawn Hill, who has been on the disabled list since June 26 with a right forearm strain, is doing well in a throwing program.
"He has no complaints," Acta said. "They'll continue to improve -- his throwing just keeps on moving forward."
The Nationals hope to have Hill back before season's end. Acta doesn't think Hill will be ready to make a rehab outing before the Minor League season ends in early September, and the skipper hasn't decided whether the 27-year-old will start or relieve if he makes it back this season.
"Our idea is [to have] him pitch here at the end of the year," Acta said.
Zachary Osterman is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.