"He'll be back soon," Harbaugh said Monday.
The Ravens are down to three healthy cornerbacks on the roster -- Lardarius Webb, Dominique Franks and Chykie Brown -- with Smith hurt and Asa Jackson on short-term injured reserve. A team doesn't want to be short-handed when facing Roethlisberger, who threw for 522 yards and six touchdowns in Sunday's 51-34 win over the Indianapolis Colts.
Smith, a 2011 first-round pick, is the Ravens' top defensive back and is one of the emerging young defenders in the NFL. He leads the Ravens with eight passes defensed and has limited some of the best receivers in the NFL, including A.J. Green, Antonio Brown, Kelvin Benjamin and Vincent Jackson.
Harbaugh declined to comment on whether the Ravens would make a move by Tuesday's trade deadline. He said the team doesn't have to add a free-agent cornerback but indicated it would be something the Ravens would consider.
"If we could find the right guy, [but] they're scarce," Harbaugh said.
Also, Harbaugh confirmed the Ravens sent in the tape of Steve Smith's offensive pass interference penalty to the NFL for review but has not heard back from the league.
"I think it shows great heart and talent and says a lot about Joe [Flacco] and Steve and the offensive line that they could make a play like that," Harbaugh said. "It was one of the greatest plays I've ever seen."