The Ravens' short-handed secondary is even thinner now, as safety Ar'Darius Washington broke his foot and is done for the year.
Harbaugh told reporters Washington suffered the season-ending injury during practice this week.
The undrafted rookie hasn't played much this season but was important depth at both safety and slot cornerback, particularly now with the Ravens banged up. Washington played a season-high five defensive snaps and 10 on special teams in Chicago.
With DeShon Elliott on IR, the Ravens are now down to just three safeties with starters Chuck Clark and rookie Brandon Stephens and Geno Stone. Versatile veteran Anthony Levine Sr. can also step in if needed, but he hasn't played a defensive snap this season.
The Ravens are also thin at cornerback this week as Anthony Averett (thigh), Jimmy Smith (neck), Tavon Young (foot/knee) and Chris Westry (thigh) are all dealing with injuries. Marlon Humphrey is the only Baltimore cornerback not on the injury report. Cornerbacks Marcus Peters, Khalil Dorsey and Iman Marshall are all on season-ending IR.
The Ravens do have a pair of cornerbacks on their practice squad: Kevon Seymour and Kevin Toliver.
Washington was a training camp and preseason standout, which made him the only undrafted rookie to make the initial 53-man roster. He played in three games and made one tackle versus the Colts.