Green Bay Packers star quarterback Aaron Rodgers injured his left, non-throwing shoulder during a 27-20 loss to the Chicago Bears.
The Packers didn't confirm reports that he broke his left collarbone on a sack by Bears defensive end Shea McClellin on the opening series.
Rodgers will undergo more tests today.
"Just had a chance to speak with Aaron; he has a shoulder injury," Packers coach Mike McCarthy told reporters. "They want to run more tests. They don't have an exact diagnosis. No timeline, no exact diagnosis."
Rodgers later today ESPN Wisconsin's Jason Wilde: "We're getting some tests."
Rodgers came back to the sideline in the third quarter with no apparent brace or sling.
He was replaced by Seneca Wallace, who completed 11 of 19 passes for 114 yards, an interception and a touchdown.
If Rodgers is out for an extended period of time, it will greatly impact the Packers' outlook in the NFC North.
A fracture could take four to six weeks to recover from.
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Aaron Wilson covers the Ravens for The Baltimore Sun.