Johnson had surgery on Thursday to clean out a "loose body" from his right elbow and will begin rehabilitation on Friday. The team said he will be out four to six weeks.
As a practical matter, the Hawks are well suited to replace Johnson because the roster has five other guards. From a statistical standpoint, the Hawks are losing a lot of production.
Johnson leads them in scoring (17.1 points), assists (5.2), and minutes (35.5), and is tops in rebounds among the team's guards (4.1). Johnson opens up the floor because of the attention he draws, and he defends point guards, shooting guards and small forwards.
Yet Johnson has struggled with his shot while taking the most attempts on the team. His 41-percent, field-goal percentage, including 26 percent on 3-pointers, is worst among Atlanta's starters.
The elbow helps explain Johnson's uncharacteristic lack of accuracy.
"With the elbow, and just watching him shoot the ball, it wasn't consistent," Hawks coach Larry Drew said. "I am glad that the problem has been identified and can be rectified. It is going to take us missing him some games but we need him back. We've got to have him healthy."
Johnson has earned a reputation for durability. He never missed a game because of injury in his first six seasons and played in a then-league best 376 consecutive games. Since sitting out 25 games in 2006-07 with calf injuries, Johnson had missed just seven games through injury.
Johnson is loathe to talk about his health setbacks, usually saying he doesn't like to make excuses. The elbow had been bothering him on and off since last season, and he finally had it examined after waking up Tuesday morning with significant pain.
Drew said he appreciates Johnson's toughness but wants players to speak up when they are hurt.
"Any kind of problem you are having, just let us know," he said. "Joe is a trooper. He is just a guy who is going to fight through most pains and hurts and injuries."
After a remarkably injury-free season in 2009-10, Atlanta's luck has taken a sharp turn for the worse.
Starters Josh Smith, Al Horford and Marvin Williams missed no games because of injury last season, and Johnson sat out just four. Among the top reserves, Crawford missed two games and Zaza Pachulia three.
This season, Evans (eight games), Williams (four) and Crawford (one) have missed time with injuries, and Johnson might sit up to a quarter of the season.
"We were really, really lucky last year," Drew said. "We didn't have guys missing extended periods of time. That hasn't happened thus far. It is all part of it. We've got to deal with it."