Smith is weighing whether or not to have shoulder surgery, according to a source. Smith and doctors are expected to decide Wednesday morning which option to take. Multiple sources say if Smith has the operation, he could be out for as long as three months. If he opts not to have the surgery, he might not miss many games but he could do long-term damage to his career after this season.
Smith, injured Sunday in Detroit, was evaluated Tuesday.
Smith has been with the Steelers (3-2) longer than any player except wide receiver Hines Ward and defensive back Deshea Townsend. He is one of the keys to their 3-4 alignment and is often cited by teammates as being the most underrated player on what was the NFL's top defense the last two seasons.
Smith has 13 tackles and two sacks in five games and blocked a field goal attempt during the Steelers' 13-10 victory over Tennessee on Sept. 10. He also is one of the Steelers' primary run stoppers.
"He's got a lot of talent," Tomlin said of Hood, the former Missouri player. "He's not out of the oven yet, if you will. We acknowledge that. He acknowledged that. And as long as we continue to do that, he'll move in the right direction. ... But by no means is Ziggy Hood a potential replacement for Aaron Smith at this point."
The 33-year-old Smith sat out the last four games of the 2007 season because of a torn biceps muscle.
Steelers safety Troy Polamalu, who has missed four games due to a torn left knee ligament, and running back Willie Parker (left big toe) are expected to return Sunday against the Cleveland Browns (1-4). Parker has missed two games.
Information from ESPN.com's John Clayton and The Associated Press was used in this report.