Anthony Rendon is not in Harrisburg’s lineup Tuesday because of tightness in his side. (Jonathan Newton/The Washington Post)

ATLANTA — Anthony Rendon seemed to be nearing a return. He was scheduled to play seven innings in Harrisburg Monday night, then nine more Tuesday. If all went well, the Nationals would soon be able to assess his readiness for a return.

All did not go well.  He was scratched Monday night, and will not play Tuesday night, either. Tuesday, the problem was a new one: “Tightness in his side,” according to Nationals Manager Matt Williams.

“He reported to the stadium and felt a little tightness kind of in his side, so we want to make sure we don’t mess with stuff like that. I think he’s fine, it’s just a question at this point of not rushing him too fast,” Williams said. “[The Class AA Harrisburg Senators] got a noon game [Wednesday], so weather will hopefully be a little warmer for him, get him going, but I don’t think it’s a huge issue. He felt it a little bit and said he was a little tight in his side [Tuesday], so given our spring training and what has happened thus far, we don’t want to take a chance. Get him some treatment, get him going again. I think he’ll be good.”

Monday before the game, the team announced Rendon had been scratched with “fatigue” and the team was taking “a cautious course of action.” After the game, Williams said Rendon had trouble loosening up his knee in the chilly weather. His left knee — the one with the sprained medialcollateral ligament from which he is trying to return — feels “better today,” Williams said Tuesday.

“Any time you’re in a situation like this, haven’t had spring training, you don’t get the benefit of those spring training days off where you can get the big treatment, so he’s kind of in that mode,” he said.

Given that center fielder Denard Span required two separate offseason procedures on core muscle injuries and that infielder Yunel Escobar missed much of spring training with an oblique strain, one can understand the Nationals’ extreme caution. Had Rendon missed another day because he was unable to get the injured knee loose, that would have been a troubling indication that the knee is not yet healthy enough for a return. So if the injury is just a tweak of his oblique, perhaps that is not so bad — relatively speaking. Rendon did not hit or field Tuesday, but underwent treatment, according to Williams.

Rendon sprained his left MCL diving for a ball against the Braves on March 9. He played five innings in Harrisburg Friday night and seven on Saturday.