LOS ANGELES — The Dodgers’ roster for the National League Championship Series against the Cubs is missing one very important piece. Corey Seager is not on the 25-man active roster for the series, out with a back sprain.

Seager felt something in his back in a slide in the first inning of Game 3 of the NLDS against the Diamondbacks, though he played the rest of the game.

“It was a very normal slide. I watched it over and over again to see if I landed awkward, hit awkward. I mean, it was extremely normal,” Seager said. “I felt it on the slide right away. Really wasn’t kind of sure what it was. Puig pulled that first ball foul and took off running, and that’s kind of when I realized something was wrong.”

The next day Seager’s back felt worse, and he had an MRI exam which showed the sprain.

“This sucks, to be honest,” Seager said.

Seager received an epidural injection from Dr. Robert Watkins in Los Angeles on Tuesday.

“His back's been barking since that Game 3 in Arizona, so we're going to have him lay low,” manager Dave Roberts said on Friday. “A lot of what we've done even this season, just keep him off the field, helps the elbow and now with the back, so to keep him laying low. But we're optimistic he'll be fine day-to-day.”

That optimism waned later on Friday night when Seager didn’t improve. He hasn’t yet been cleared to run or hit, which would only be the first hurdle he needs to clear before being activated.

Roberts couldn’t say whether Seager might be ready for activation at some point during the NLCS, or even if he would be ready for the World Series, should the Dodgers advance.

“It’s all contingent upon his health, so right now he would be,” Roberts said. “But in the coming days, the next couple days, if it continues to improve and we can test them and he can pass some tests, that’s a different story. So a couple things right there have to happen for us to even entertain that.”

Seager will not travel with the team to Chicago for the middle games of the series.

“I think next week is going to be kind of a big week to see if I can get back into baseball activities and stuff,” he said. “I'm progressing every day, which is really nice. But I'm not really sure.”

With Seager out, Charlie Culberson was added to the Dodgers’ roster, though the bulk of playing time at shortstop — at least against right-handers — figures to go to either Kiké Hernandez or Chris Taylor, both of whom took ground balls at shortstop during workouts at Dodger Stadium the last two days, along with Culberson.

Culberson starts at shortstop in Game 1 against left-hander Jose Quintana.

The roster scramble means the Dodgers needed another outfielder, so Joc Pederson was added to the NLCS roster. Pedro Baez, who did not pitch in the Division Series against the Diamondbacks, is off the NLCS roster.

The Dodgers have 14 position players and 11 pitchers on their roster for this series. They had 12 pitchers in the NLDS, and had 12 pitchers on last year’s NLCS roster against the Cubs.

The Cubs have 11 pitchers and 14 position players on their NLCS roster. The only change from their Division Series roster is right-hander Hector Rondon replacing left-hander Justin Wilson in the bullpen. That leaves Chicago with two left-handed relief pitchers — Mike Montgomery and Brian Duensing.