Several Ravens players were affected by a cold that swept through their building last week, including Jackson, wide receiver Rashod Bateman and center Bradley Bozeman, among others, a source told Schefter.
Jackson, who is listed as questionable, was added to the report as a precautionary measure because he wasn't feeling 100%, a source said. Jackson does not have COVID-19, according to a source.
The Ravens also downgraded wide receiver Marquise Brown to out with a thigh injury. He had missed two practices this week before being limited Friday.
Jackson returned for a full practice Friday after missing two days with an illness. He did not carry an injury designation after Friday's practice and said with a big smile that he was "feeling great."
Jackson has missed only two games in his four-year NFL career. He sat out the 2019 season finale because Baltimore had already secured the No. 1 seed and was held out of a Week 12 game in 2020 after testing positive for COVID-19.
The AFC North-leading Ravens (6-3) are coming off a 22-10 loss at the Miami Dolphins, scoring their fewest points with Jackson as a starter. After Sunday's matchup with the Bears, Baltimore doesn't play another team with a losing record for the final seven games.