The 26-year-old, whose sole England cap came in a World Cup warm-up against France in August, has not played since suffering the injury in a pre-season match against Wasps in October.
"We were hoping he'd recover from his injury," Saints coach Jim Mallinder told BBC Radio Northampton.
He also said Courtney Lawes and Alex Corbisiero could return in a few weeks.
Northampton Saints flanker Calum Clark will be out for at least two months after having shoulder surgery.