"He hurt his knee. We'll see where it is," Schwartz said. "He wasn't able to go back in and finish. We tried to get a sleeve on it, we tried to get a brace on it. It was a situation where it was still possible if he could feel good with it he could go back in the game. ... We just couldn't get him comfortable."
Johnson, who was limited in practice all week because of a thigh injury, tweaked his knee while running a route across the end zone during the first quarter. He pulled up and appeared to be in pain. He left the field and had his knee treated on the sideline.
Johnson has 22 receptions for 325 yards and one touchdown this season. His departure from Sunday's game left Detroit without two of its top offensive players, as rookie quarterback Matthew Stafford was sidelined because of a knee injury.
Schwartz also said cornerback Eric King (shoulder), defensive end Jason Hunter (ankle) and fullback Casey Fitzsimmons (thigh bruise) left the game with injuries and did not return.
The Associated Press contributed to this report.