Smith also confirmed that tight end Desmond Clark will not play Sunday because of a rib injury. He'll be replaced by Kelvin Davis.
Smith has been impressed with Bowman, who played about 12 snaps at cornerback in the season-opening loss at Green Bay after dealing with a pulled hamstring in training camp.
"I thought he played well in the limited time he had the other day (against the Packers)," Smith said. "We have been bringing him back from an injury. He's done a lot of good things when he's had an opportunity to play."
Vasher, a regular Bears starter since 2004, has 18 interceptions in his six-year NFL career and received a five-year, $28 million contract extension from the team in 2007.
"I just have to continue to keep working and do the things I've been doing and try to help Zack out as much as I can and be a total team player," Vasher said.
Manning had a pulled hamstring through much of training camp and preseason, but he played nickel back against Green Bay. Although he's healthy enough to resume his old starting job, Manning expects to be tested by the Steelers.
"I'm quite sure they're going to throw deep a lot, especially me coming back from a hammy injury they're going to try to go deep," Manning said.
Copyright 2009 by The Associated Press