Coach John Harbaugh said Wallace suffered a minor knee sprain during Thursday's preseason win against the Titans, Jamison Hensley of ESPN.com reports.
Wallace managed to reel in one of two targets for three yards and tally one carry for minus-four yards before departing in the first quarter. He picked up the knee issue on the aforementioned end-around, after which he went to the blue medical tent and didn't return. The decision may have been one of precaution, and Harbaugh told Jeff Zrebiec of The Athletic that he's unsure how much time Wallace may miss.