Nate McLouth. (AP Photo/David Goldman)

Nate McLouth was scratched nearly 30 minutes before first pitch on Sunday in Atlanta after an old injury in his left knee flared up while he was making throws in the outfield. McLouth, 32, said he has dealt with patellar tendinitis for years and knows how to calm it. But while throwing, perhaps he planted unusually and the injury “flared up pretty bad.”

“I knew I couldn’t play an effective outfield and it wouldn’t have been good for anybody,” he said. “Just decided to not play [Sunday] and that was definitely the best thing. But it’s something I’ve dealt with for a long time and can always manage. It just flared up unfortunately right before a game.”

McLouth said the discomfort comes and goes, but he is always able to manage it enough to play. He said he hopes the pain subsides by Sunday night so he can play Monday night. “We’ll play it by ear,” he said.

“I don’t think it’s anything serious,” Manager Matt Williams said. “He was just sore. We had him looked at by the doc.”

McLouth is a primary option to play the outfield alongside Bryce Harper and Jayson Werth while center fielder Denard Span is on the seven-day concussion disabled list. If there are any setbacks with McLouth, the Nationals could turn to a combination of Steven Souza Jr., Tyler Moore and Kevin Frandsen.