The five-time Ballon d’Or winner has been unable to play a full part in training over recent days.
He will not be risked in a Serie A clash between two top-four chasing sides.
Andrea Pirlo does have plenty of alternatives at his disposal, though, and is planning on handing a starting berth to Paulo Dybala.
Dybala has not figured from the off for Juventus since January 10 due to a knee problem.
Pirlo’s say on Ronaldo injury
Pirlo announced Ronaldo’s injury news at a press conference ahead of a crunch clash with Atalanta.
“Cristiano Ronaldo has a problem with his thigh flexors, he won’t be there against Atalanta.”
“We will try to recover him for Wednesday against Parma.”
“He wasn’t able to ‘push’ the way he wanted to in training this week and we prefer not to risk it.”
“The internationals didn’t help, he’s been playing a lot lately.”
“Paulo Dybala will start tomorrow,” he added.
However, Pirlo is expecting to be in a position to call upon Weston McKennie and Arthur against Atalanta.
The American and Brazilian midfielders have been able to overcome slight knocks.
Juventus sit third in the Serie A table as things stand, with a 12-point gap separating them from leaders Inter with only eight games left.