Saints lock Courtney Lawes says he expects to return to action in four to six weeks.
Lawes has been sidelined since suffering an ankle injury in the victory against Leicester Tigers at Franklin’s Gardens on December 20.
He had remained hopeful of a quick return, but was eventually sent for a scan and forced to undergo surgery last Monday.
It means he will not be available for England’s Six Nations opener against Wales on February 6, with the game in Ireland on March 1 his most optimistic target.
“I’m looking at four to six weeks left so best case scenario will be that in four weeks’ time I’ll be back playing,” Lawes said on talkSPORT’s Full Contact programme.
“I did it in the Leicester game before Dylan (Hartley) got sent off, so really early, and I played the rest of that game with it in quite bad shape.
“Because I managed to get through the game, it was treated as less of an injury and more of a niggle.
“I spent the best part of a month icing it. I’d be put on the bench every week and I’d fail a fitness test every week trying to get back fit.
“It got to the point where we realised it wasn’t going to get any better so I got in for a scan and there was more damage than we thought.”