Coach Mike Tomlin said after the game that Haden broke his fibula and is out indefinitely.
"Joe Haden has a fibula fracture," Tomlin said. "It's high on his leg. I don't know what that means."
Haden underwent a scan that showed a non-displaced fracture of the fibula head and no surgery is required, according to a source. Haden is bracing to be out 5-6 weeks, but knows it could be sooner, per the source.
The Steelers are outlining his recovery plan and it "Could have been much worse," the source said.
Haden collided with a Colts offensive player late in the first quarter and was down on the Lucas Oil Stadium turf for a few minutes. Haden walked off the field without a limp and went to the locker room. Veteran Coty Sensabaugh replaced him in the lineup.
Haden, a longtime member of the Cleveland Browns who signed a three-year, $27 million contract with the Steelers in August, helped stabilize a much-improved secondary and second-ranked defense. The Steelers' secondary gave up touchdown passes of 60 and 61 yards against Indianapolis after Haden left the game.
In addition to Sensabaugh, the Steelers can also activate third-round rookie Cam Sutton off injured reserve.