The team announced Thursday that Horford tore his left pectoral muscle in the first quarter of Wednesday night's game at Indiana. The injury will likely require surgery, stunning a team that has made the playoffs four years in a row and is off to a solid start with wins over Miami and Chicago in the early going.
"I did hear something kind of pop a little bit, so I thought it was something different," said Horford, who wrenched his shoulder while battling for a rebound with Roy Hibbert. "I'm still surprised. I thought I was going to be able to rehab it for a couple of weeks and come back."
Horford, a two-time All-Star, could be out as long as four months, which would take his rehab deep into the playoffs -- should the Hawks make it that far. He will get a second opinion before making the final decision to undergo surgery, but even the most optimistic projection would keep him out until mid-April.
The Hawks final regular-season game is April 26.
"He's going to certainly be missed," coach Larry Drew said. "We were starting to mesh. We were starting to jell. I'm hoping our guys will rally around one another."
Horford was injured with 6:08 remaining in the first quarter of Wednesday's game. He was averaging 12.4 points, 7.0 rebounds, 2.3 assists and 1.3 blocks to go along with the NBA's eighth-best shooting percentage (.553).
The 25-year-old is a bit undersized for the center position (6-foot-10, 245 pounds) but he quickly emerged as perhaps the most valuable Atlanta player after being picked third overall in the 2007 draft. His loss leaves the Hawks with a huge hole on the inside, plus some much-needed leadership in the locker room. Zaza Pachulia and Jason Collins are the other centers on the roster, neither of whom is likely to come close to matching Horford's production.
"The talent is huge," Drew said. "But the leadership and the presence, he's the glue for us."
"Guys are going to have to pick up the slack," Horford said. "The guys are going to have to raise their games. It starts with Josh and Joe."
Johnson, who is leading the Hawks with 16.7 points a game, is ready to take on more of a load but said he can't do it himself.
"We can't worry about who we have out on the court, we've just got to go out there and play," Johnson said. "Not only I have to step up, but the whole locker room. Our big guys have to step up to fill that void of losing Al."
Smith said he'll miss working with Horford on the inside.
"That's a big void," Smith said. "Me and him are like the bash brothers down there in the paint. It definitely, definitely, definitely was very disappointing."
But no one is giving up on making the playoffs. When Smith was asked if the Hawks were capable of making another trip to the postseason without their All-Star center, he quickly replied:
"Yeah. Most definitely."