Koetter said the Buccaneers decided to shut down Winston after the third-year quarterback underwent an MRI on Monday. Koetter declined to discuss specifics on the MRI findings.
"They're saying this is not structural, but they want to shut him down," Koetter said. "Right now they're saying at least two weeks."
Winston said Sunday that he did not aggravate the sprained AC joint that had nagged him for the past three weeks, saying it was the same injury. He had taken multiple hits the past three weeks, but one particular hit before halftime Sunday, when he was sacked by Cameron Jordan and Alex Okafor, did him in.
"When he got hit on his left side and the weight of the defensive end and Jameis' weight fell on his right shoulder, that's when he aggravated it," Koetter said. "After that point, he was definitely hurt."
Koetter said the Buccaneers would activate Ryan Griffin to serve as Fitzpatrick's backup against the Jets.