Cervelli suffered a concussion as a result of a collision at home plate on Sept. 8 in Baltimore.
He has not played since that day due to the lingering effects of the concussion, the third one Cervelli has suffered in his career.
He underwent an IMPACT Test on Monday, which compares results with tests taken when his head isn't affected by an injury. Cervelli is also scheduled to see a neurologist on Friday.
"He's still experiencing symptoms so I'm not sure we're going to get him back," Girardi said, giving the strongest indication to date that Cervelli will not be available for the postseason.
Cervelli, hitting .266 with four home runs and 22 RBIs, will likely be replaced by September call-up Austin Romine, who is considered a strong defensive catcher.
When speaking to reporters on Monday, Cervelli said he hadn't felt any symptoms in three days. Apparently, the results of the IMPACT Test showed otherwise. Girardi reported on Tuesday that Cervelli was indeed still feeling the effects of his collision with Orioles right fielder Nick Markakis.
"He's not ready to do any baseball activity," the manager said.
Cervelli also said on Monday that he prays "every day" that he will be able to return this season.
As for Romine, he said he is solely focused on handling the pitching staff during games he's called on to catch over the remainder of the regular season. Romine, of course, added that he would welcome the opportunity to catch in the postseason.
"It comes in your mind, but if it happens it happens," Romine said. "I have to worry about right now because if I don't prove I can catch right now then they're definitely not going to take me in the postseason."
Romine entered Tuesday hitting .143 in seven at-bats over three games since being called up. He batted .286 in in 85 games in Double-A Trenton.
Ian Begley is a regular contributor to ESPNNewYork.com.