Ryan Zimmerman is officially day-to-day after injuring his left oblique against the Mets over the weekend. (Jeff Roberson/Associated Press)

MIAMI — Nationals first baseman Ryan Zimmerman insists he’s still day-to-day. He is battling left oblique soreness but remains hopeful it will subside enough to let him return soon. He injured the muscle on a swing last weekend and played through the trouble on Monday. He said he hasn’t had an MRI, but he hasn’t swung a bat since Monday, either.

“Just started off small and has gotten worse. Still kind of just a day-to-day thing,” said Zimmerman, whose name was on the Nationals lineup card as an option off the bench, though the chances of him hitting Friday night are slim at best. “Hopefully it continues to get better, but there’s no way to know but to wake up and come here and see how it feels.”

That Zimmerman is traveling with the team indicates that he is likely not entirely shut down, though the Nationals would not necessarily need to say so if he is: Since rosters are more flexible after September expansion, they do not necessarily need to place Zimmerman on the disabled list. Oblique injuries, officially diagnosed, cost Yunel Escobar, Anthony Rendon and Stephen Strasburg disabled list stints of about a month each. Should Zimmerman’s do the same, he would miss the rest of the season.

“We know there’s something wrong,” Zimmerman said. “It’s one of those things where I really don’t have an answer. I wish I did. It’s about as day-to-day as it can get.”

Zimmerman is undergoing treatment, the goal of which is to help Zimmerman get to the point where he can swing a bat again, according to Manager Matt Williams. At that time, he may be able to return. Zimmerman said he would have no problem returning even after a week lost to inactivity, so not swinging for a few days is not necessarily a huge problem.

“I think they always look out for the best interests obviously of us, but time isn’t on our side. But there’s no reason to go out there and play if you have a chance of seriously injuring yourself or obviously not being able to play to the level you should be able to play,” Zimmerman said.

Zimmerman battled plantar fasciitis in his left foot, which arose in April and forced him to the disabled list in June. He returned in late July and by the end of August was one of the hottest hitters in baseball. (As of his last game Monday, Zimmerman was on an 11-game hit streak during which he was hitting .435 with four doubles, six homers, and 18 runs batted in.)

“Anytime you have to miss games it’s not fun. I guess it’s part of it,” Zimmerman said. “… I was playing really well, finally felt healthy, foot was feeling pretty good. But that’s part of it.”