On December 10, 2011, following the conclusion of the NBA lockout, Green re-signed with the Celtics. Eight days later, his contract was voided by the Celtics after a routine physical examination detected an aortic aneurysm. He subsequently underwent heart surgery in January 2012 and missed the entire 2011–12 season. Former teammate Kevin Durant dedicated his season to Green. Green used his downtime not only to rehab from surgery but to complete his coursework at Georgetown, graduating in May 2012 with a degree in English and a minor in theology.