Bench coach Randy Knorr handled the rest of the game, which the Nationals won, 5-1, to clinch the National League's top seed heading into this weekend's NL Division Series.
"About the third inning of the game, I started losing all feeling in my left leg," Johnson said. "Just numb. I took a muscle relaxer at that time and a heavy dose of aspirin, and about the seventh inning, it didn't let up."
By the time he spoke to the media after the game, Johnson said the numbness -- which he attributed to narrowing between his L3 and L4 vertebrae -- had not subsided, but he was confident it would shortly.
"All the nerves that come through, and the disc, when it narrows, it bulges, and that can press against nerves. So what they try to do is calm that area down," Johnson said. "It's nothing more than they can give me an injection in that area, but before we do that, I'm on a heavy dose pack to knock out the inflammation and swelling."
The 69-year-old skipper expects to be at full strength when the Nationals travel to either St. Louis or Atlanta on Saturday morning in preparation for Sunday's Game 1 of the NLDS.
"I just didn't wanna embarrass myself if my leg gave out," Johnson said. "Didn't feel that was a good idea."