Green is not expected to be ready for the regular-season opener Sept. 8 at Seattle.
He was carted off the field Saturday during the Bengals’ first training camp practice of the season at Dayton’s Welcome Stadium.
The Bengals were practicing at Welcome Stadium as part of the NFL’s 100th anniversary celebration. The conditions of the field were considered subpar.
Green’s left shoe was removed before he departed the field. Last season, he missed seven games with a right toe injury.
That campaign marked only the second time Green did not have at least 1,000 receiving yards in a season during his eight-season career. Green, a seven-time Pro Bowl selection, participated in Bengals minicamp in June.
He is entering the final year of his contract.
ESPN’s Ben Baby contributed to this report.