Hernandez's absence would force the Patriots to adjust without one of their best offensive weapons. There is not an exact timetable for Hernandez's return, but the star tight end will not play against the Baltimore Ravens in Week 3, the source said.
According to the source, Hernandez likely will not return until October at the earliest. Patriots coach Bill Belichick said during Monday's news conference that he did not have an update on Hernandez's status.
Hernandez suffered the injury in the first quarter of Sunday's loss to the Arizona Cardinals and left the stadium using crutches and wearing a walking boot.
The Patriots must find a better way to adjust without Hernandez in the lineup. New England's offense looked lost without its vaunted two-tight end set against the Cardinals and didn't score a touchdown until late in the fourth quarter.
Hernandez had six catches for 59 yards and a touchdown in New England's season opener following a breakthrough 2011 campaign during which he caught 79 passes for 910 yards and seven touchdowns. He signed a five-year, $40 million contract extension with the Patriots in August.
ESPNBoston.com's Mike Rodak and Field Yates contributed to this report.