"I think we've been staying afloat, especially with all the injuries we have currently," Hairston said. "That's the sign of a good team. The depth of the organization, guys who are coming up and making contributions, it's been really helpful. I think once we piece things together, once we get everybody healthy, we'll be the team that we're expected to be."
Hairston played in only two games before the injury and went 1-for-2. He spent a three-game rehab assignment at Syracuse, going 1-for-10 with a double, two walks and four strikeouts.
"I played nine innings a couple of games and felt good," he said. "Just working out the timing as a hitter, that's always the biggest challenge."
With Harper out, Hairston could see some starts in left field against left-handed pitchers. That could be as early as Tuesday, when Washington faces Dodgers ace Clayton Kershaw.
Nats manager Matt Williams has been using Tyler Moore and Kevin Frandsen as right-handed bats in left field, but Frandsen has played mostly infield in his career, and Moore could be needed at first base, with Adam LaRoche nursing a sore quad.
"It's a veteran right-hander off the bench," Williams said of Hairston. "It's power. He certainly matches up well against left-handed pitching."
In more than 1,000 career plate appearances against lefties, Hairston has posted a slash line of .269/.317/.498, with 49 home runs.
This was Souza's second short stint with the Nationals this season. The 25-year-old rookie got his first and only big league start last Wednesday in Houston but otherwise has come off the bench, going 1-for-8 with a walk.
Andrew Simon is a reporter for MLB.com. Follow him on Twitter @AndrewSimonMLB. This story was not subject to the approval of Major League Baseball or its clubs.