Estrada has been having problems with the elbow since early in camp, and he has not played in an exhibition game.
"We don't see Johnny making the Opening Day roster -- no way," Acta said.
General manager Jim Bowden is likely to wait until the end of Spring Training to make sure that Estrada is not ready to play.
"I don't ever like to disable [players] prematurely," Bowden said. "If something miraculous happens, I don't want to regret it a week later, so we'll be conservative."
With Estrada out to start the season, Wil Nieves will most likely serve as the backup catcher. Acta and Bowden said that Jesus Flores most likely will be an everyday player for Double-A Harrisburg.
Meanwhile, Elijah Dukes (right hamstring strain) played Friday for the first time since late last week and went 1-for 3 against the Mets. In the first inning, Dukes doubled to left field and still had problems with the hamstring.
"I felt pretty good in the beginning, and then it started to get a little sore on me," he said. "But I was able to pull through five innings."
Dukes said he does not expect to play against the Braves on Saturday.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.