Anthony Rendon will sit once again. (Rob Carr/Getty Images)

CHICAGO — If there is anything the Washington Nationals have learned this year, it is that a seemingly small problem does not necessarily stay that way, particularly when it comes to injuries. Earlier this year, for instance, Anthony Rendon fouled a ball off his foot and, after an optimistic diagnosis that seemed unlikely to require him to spend time on the disabled list, it was announced that he had a fractured toe that required weeks to heal.

So when Rendon took a pitch off the left wrist in Friday’s loss to the Chicago Cubs and continued to play, Manager Dave Martinez initially said his third baseman was fine. As far as Martinez knew, after watching Rendon play the rest of that game, he was.

But Rendon was a late scratch from Saturday’s lineup and is not in the Nationals’ lineup for their series finale with the Cubs on Sunday night. Initial X-rays were negative, but the problem — officially a left wrist contusion — is obviously lingering. Rendon was not in any kind of splint or cast Saturday. But whatever the problem is, it is enough to keep one of the Nationals’ key right-handed bats out of the lineup as the Nationals take on recently acquired Cubs left-hander Cole Hamels.

“He’s better. He’s still pretty sore,” Martinez said. “So instead of taking a chance and running him out there for four at-bats, we’ll give him another day. In an emergency, he’s available.”

Martinez said Rendon is all but entirely uninhibited defensively and could be available to help on that front late in Sunday’s game. But when he swings and misses, the wrist hurts, so Martinez decided against risking that Sunday evening.

“I’m hoping that tomorrow he’ll be ready to go,” Martinez said.

In other Nationals injury news, closer Sean Doolittle threw on flat ground before Sunday’s game, testing his back foot by going through his motion and loading over his back leg. That left foot is hobbled by a stress reaction that has not dissipated, but that Doolittle says is improving. He is currently in the process of pushing it little by little to see what the foot will tolerate, then judging his progress based on how he feels the next day. In keeping with that process, Doolittle also did dry work — simulating his motion without throwing — on a mound Sunday. He said he had no problems.

“I’m working on some really minor mechanical adjustments with my lower half to try to take some of the stress off that area of the foot,” Doolittle said. “So it’s the next step in building that trust. I still feel it, but I need to know … you’re going to feel it and it’s okay. You’re not going to make it worse. Even if it’s really sore afterward, I’ve had days where the next day it bounces back and feels good.”

Doolittle said he can’t be sure he won’t make the problem worse by testing it, but that over the last few days, he is noticing he can use his back side more freely. As long as he continues to bounce back after sessions like Sunday’s, he will consider that progress. As of Sunday afternoon, Doolittle thought he would be able to move to a mound as soon as Monday or Tuesday.

Once he can throw freely, without altering his mechanics or compensating for that back foot, Doolittle shouldn’t need much time to build back up before returning to the bullpen. He has been throwing ever since suffering, even if only with his top half, so his arm is still in shape.

“If it’s going to be good enough to push off a mound,” Doolittle said. “It better be good enough to do everything else I have to do.”

WASHINGTON NATIONALS (60-57)

Trea Turner SS

Juan Soto LF

Bryce Harper RF

Ryan Zimmerman 1B

Daniel Murphy 2B

Mark Reynolds 3B

Michael A. Taylor CF

Matt Wieters C

Max Scherzer P

CHICAGO CUBS (67-49)

Anthony Rizzo 1B

Javy Baez 3B

Ben Zobrist 2B

Jason Heyward RF

Albert Almora Jr. CF

Kyle Schwarber LF

Willson Contreras C

Cole Hamels P

Addison Russell SS

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