Hawks point guard Mike Bibby has also been sidelined with an ingrown toenail.
Johnson didn't travel with the Hawks, who play Tuesday in Charlotte and Wednesday in Detroit. He sat out Saturday's win against the Pistons after getting hurt last week against the Los Angeles Lakers.
Maurice Evans is expected to start against the Bobcats.
Bibby was scratched after he said he couldn't participate in Tuesday's shootaround. He says a doctor took off most of the right side of his big left toenail on Monday because of a concern over a possible infection. He says he hopes to play Wednesday.
The Hawks entered the night one game ahead of the Boston Celtics with six games left in the race for the No. 3 seed in the Eastern Conference playoffs.
Bobcats coach Larry Brown didn't know if center Theo Ratliff would return to face Atlanta. He's been away from the team after the death of his grandmother. Brown said Tyson Chandler would start in his place.
Information from The Associated Press was used in this report.