Smith, an elite 3-4 defensive end and one of the key cogs in Pittsburgh's defense, tore his triceps during a Week 7 game at Miami and hasn't played since.
The Steelers knew at the time that Smith's injury could have been considered season-ending, but given his importance to the team, they kept a roster spot open for the playoffs and didn't place him on injured reserve. He is virtually certain not to face the Baltimore Ravens this week and would be doubtful to play in the AFC Championship Game as well, according to the source.
"The Super Bowl would probably be the most realistic timetable," the source said.
Smith resumed weightlifting weeks ago, but he has only been able to practice thus far on an extremely limited basis.