Anthony Rendon. (Jonathan Newton/The Washington Post)

LAKELAND, Fla. — When Anthony Rendon made a brilliant diving stop last Monday, he knew he’d banged his left knee hard. But he’d done that before — it’s part of the job — and played through the bruises that followed. So he didn’t worry much.

After the game, his knee grew sore, so Rendon hopped into a cold tub. By the time he got home, he felt the pain as he walked around his apartment, so he started to worry. He told the Nationals’ staff the next morning, and they sent him to get an MRI.

“It was pretty painful that night,” Rendon said. “I didn’t know what to expect.”

The picture revealed a sprain of his left medial collateral ligament, one manager Matt Williams initially said would keep him out a few days. A week later, Rendon is still inactive, resting the injury and not free of soreness. While the whole thing escalated more sharply than he initially anticipated, Rendon says he doesn’t anticipate a lengthy absence — but he doesn’t know when he’ll be back either.

“I’m feeling all right,” Rendon said. “Just taking it day by day, I’m still a little sore, but we see how it is each and every day. It’s not something you fix overnight.

“I know it’s not going to be like weeks, weeks, weeks and months. Well, I hope not — barring any setbacks. I think I should be out there not too long from now.”

Rendon said doctors compared the injury to rolling an ankle, a comparison that partially explains the uncertain timetable: Severely sprained ankles can cost professional athletes weeks, while lesser sprains can take only days. But even if the injury is not a long-term concern — and he says he is “not worried about it now” because he knows what it is — the sprain has cost Rendon more than a week of spring training at-bats, with more likely to come.

“It’s definitely frustrating. It is hard. Experiencing it in the past, having a past injury history, I know how to handle it so I’m more relaxed,” said Rendon, who battled ankle injuries in college and in the minors. “You really can’t do much. You just have to move on, move forward from it and look at the positives.”