Johnson, a four-time All-Star with averages of 17.1 points, 5.2 assists and 4.1 rebounds in 18 games this season, had successful surgery on his right elbow on Thursday and is expected to miss anywhere from 4-to-6 weeks.
His absence didn't stop the Hawks from winning their fourth straight on Wednesday when Mike Bibby made three of his four three-pointers in the fourth quarter, as Atlanta held off the Memphis Grizzlies, 112-109, at Philips Arena.
Bibby finished with 15 points and six assists for the Hawks, who found out before the game that Johnson would be sidelined up to six weeks.
"I think we have enough off the bench," Atlanta head coach Larry Drew said. "We have guys that are capable. We just have to get some guys to step up a little bit more."
Al Horford added 20 points, six rebounds and six assists for Atlanta against Memphis. Jamal Crawford and Josh Powell each chipped in with 16 points, while Marvin Williams tallied 15 points for the victors.
The Sixers, meanwhile, have shown a little life recently, winning their second consecutive contest on Tuesday when Elton Brand scored 18 points and Philadelphia stepped up the defensive pressure in the fourth quarter to down Portland, 88-79, at the Wells Fargo Center.
Jrue Holiday donated 11 points as did Andres Nocioni off the bench for the 76ers, who have won consecutive games for the first time since March 24-26, 2010. Spencer Hawes chipped in 10 points in the victory.
"It was just a great win," said 76ers head coach Doug Collins. "I am so pleased with how our guys are playing defense."
The Hawks' current four-game run is their longest since opening the season with six straight victories, one of which was a 104-101 victory at Philadelphia on Oct. 29.
"They have so much offense," Collins said of the Hawks to the Sixers' official website. "They have a lot of fire power. They are very athletic."