(Photo by Katherine Frey/The Washington Post)

Nationals first baseman Adam LaRoche exited the Nationals’ 6-4 victory Monday night in the seventh inning with stiffness in his lower back, an ailment that held him out of a game last week in Philadelphia and could sideline him during the Nationals’ final two games in Los Angeles.

LaRoche said he considers himself “day-to-day,” and Manager Matt Williams said LaRoche could “potentially” sit Tuesday night against Clayton Kershaw. LaRoche plans to take medication to alleviate the pain, and he hopes it will allow for a quick recovery.

“It’s been tight for a while,” LaRoche said. “It’s gotten later in the game. In the fourth, fifth inning, it starts really tightening up from just standing around. I’ve had it before. I hope it’s quick, a day or two. But you never know.

“It’s one spot in my lower back that locks up. I’m able to get it pretty loose to get going. The further along the game goes, the more standing out there at first, defensively, is when I feel it the most. Yesterday was really sore, and today the same thing.”

LaRoche’s back stiffened on the Nationals’ bus ride to Philadelphia last week. LaRoche, the Nationals’ cleanup hitter, is batting .257/.361/.437 with 19 homers and 70 RBI this season. As LaRoche has dealt with the back issue, his production has waned. On the Nationals’ current road trip, LaRoche has gone 1 for 23 with a walk, an RBI and six strikeouts.

In Philadelphia, LaRoche said his experience with back stiffness would allow him to manage the injury. Now, he still believes it will not be a long-term problem, but he’s not sure if he’ll be able to play in the near future.

“I’m not concerned that this could drag out for a while,” LaRoche said. “I don’t know that I’ll be able to play through it. Right now, I tried today. Yesterday was rough. Today, the game plan was start the game, hopefully finish, worst-case get a lead and find a point to come and get some ice on it.”

Monday, Kevin Frandsen replaced LaRoche as a pinch hitter and played the final three innings in the field. If LaRoche cannot play against Kershaw, either Frandsen or call-up Tyler Moore would get the start.

“It’s never a good time to have it happen,” LaRoche said. “But it’s nice now we got some reinforcements in with call-ups, to where I’m not handcuffing the skipper with having to make a tough decision.”

LaRoche said simply taking a few days off wouldn’t necessarily eliminate the pain in his back. “I don’t know that it’s that type of injury,” LaRoche said. “I don’t know that it can get worse, knock on wood.”