"Ben Foden sustained significant damage to his ankle ligaments during last Friday's Aviva Premiership Rugby game against Bath and is going to see a specialist tomorrow," read a statement from Northampton.
"The club will have more information after that, but Ben is expected to be out of action for a number of weeks."
Foden turned awkwardly as he was hit hard by Bath wing Tom Biggs in the 45th minute of Northampton's 18-14 win at The Rec.
He was immediately strapped up by doctors and physios at the scene but not before he had shown the Saints replacements a bump the size of a cricket ball on his right ankle.
Northampton director of rugby Jim Mallinder said at the time that he was 'hopeful it's not broken', with the club optimistic that it might have just been a strain and severe bruising despite the fact that Foden left the West Country in a surgical boot.
That isn't the case, though, and Foden now faces what could be a lengthy spell on the sidelines.
England begin their autumn campaign against Fiji on November 10, before playing Australia, South Africa and New Zealand in successive weeks.
Foden will be desperate to play some part in those fixtures, especially given the fact that full back has become such a competitive spot in the England squad.
The 27-year-old former Sale star has been one of his country's most consistent performers over recent seasons but the form of Mike Brown and Alex Goode means he is no longer a shoe in for the No15 shirt.
And it's not just with England where competition for the full back slot is so fierce.
Rob Kearney, Leigh Halfpenny and Stuart Hogg are all realistic contenders for a place in the Lions party that will travel to Hong Kong and Australia next summer, meaning it's even more important than ever that Foden returns to action sooner rather than later.