“It just started to tighten up on me,” LaRoche said. “It’s been going on probably a week or so.”

LaRoche said he had “no clue” if he would be able play to after the Nationals’ day off on Monday, when they open a series Tuesday at Nationals Park against the reeling Phillies.

LaRoche has played in 95 of the Nationals’ 101 games this year, including the past 28 in a row. He had been able to play through the stiffness before Sunday, and he suspected the early game exacerbated the injury.

“I’ve had time during the day, more moving around, loosening up, getting treatment, lot of swings,” LaRoche said. “I felt it was kind of going the other direction today. The more I stood around in the field, sat on the bench, the tighter it was getting. Hopefully, tomorrow, having the day off, I’ll have it feeling better.”

Even if LaRoche does not play Tuesday, he’s confident the injury will not hold him out a significant portion of games. LaRoche has no nerve damage, and the soreness in his back isn’t indicative of anything but muscle discomfort.

“I don’t think it’s serious,” LaRoche said. “The doctor came and looked at it. He said there’s nothing shooting down my leg or anywhere else. It’s staying in the middle of my lower back.

Despite feeling stiffness, LaRoche lined an opposite-field single to leadoff the fourth inning. “That’s the good thing,” LaRoche said. “This whole week I’ve had it, it hasn’t hurt to swing.”

When LaRoche came out of the game, Tyler Moore entered at first base. Later, Moore came out of the game in a double switch and Michael Morse took over at first for the final innings.

The Nationals have ample depth if LaRoche misses a few games, but they would miss his bat in the cleanup spot. This season, LaRoche is hitting .265/.342/.499 with a team-leading 19 homers and 61 RBI.