Smith was a Pro Bowl tackle for the Pittsburgh Steelers in 2005, but injuries limited him to 17 games over the past two seasons. A back injury sidelined him last season for the final 11 regular-season games and the Steelers' run to their sixth Super Bowl title.
The Steelers don't plan to re-sign Smith, who spent all nine of his NFL seasons with the club.
The 49ers planned to interview Smith before a medical exam. If he's healthy, the Oakland native could be a candidate to take over at right tackle for Jonas Jennings, the oft-injured starter who isn't expected to return.