Nationals manager Dave Martinez announced Sunday that Scherzer was scratched from his start against the Houston Astros because of neck and back spasms.
"[Saturday] he had a little bit of spasms in his right trap and neck," Martinez told reporters Sunday. "They treated it. He woke up today a lot worse. So Joe Ross will start today.
"And if you all know Max, obviously he pitched with a broken nose, he's been hurt before, he's gotten through things. When he comes in and says he's hurt this bad, he's hurt. And I can tell you now he's very upset. He wants to be out there with his teammates."
Martinez said that Scherzer began to experience pain when waking up Saturday and it worsened overnight into Sunday. After the injury didn't improve following treatment from the Nationals' medical staff, Martinez opted to replace him.
"I woke up this morning completely locked up. I couldn't even dress myself," Scherzer said Sunday. "I've pitched through so much crap in my career that would be easy to pitch through at this point. This is literally impossible to do anything with.
"I'm just hoping that the doctors are right and something could be possible for Game 7."
Ross will face Astros ace Gerrit Cole in Sunday night's game, with the best-of-seven series tied at two games apiece. Ross has made only one appearance this postseason, coming out of the bullpen during Game 3 of the World Series on Friday.
Martinez said he expects Stephen Strasburg will take the mound for Tuesday's Game 6 in Houston.