The 26-year-old limped off after just 17 minutes in the draw with Wigan after being injured in a challenge with Lee Cattermole.
He was certainly missed as Newcastle put in a shocking first half performance, as they lost all shape and ballance struggling to come to grips with the change.
Major Blow To Kinnear!
Barton left St James' Park on crutches and underwent scans on Sunday which revealed he had suffered a slight tear to his right medial ligament.
NUFC spokesman: "After further assessment today following scans yesterday, he has damage to his right medial ligament and will be out for eight weeks."
Barton: "I am not blaming Lee Cattermole in any way for this injury. It was a 50-50 ball and we both went for it, and these things happen.
"Obviously, it's disappointing and frustrating, and my sole intention is to knuckle down and bounce back and get fit again to help the Newcastle United cause."