Saints co-captain Dylan Hartley will miss the rest of the Six Nations after it was confirmed that he will have knee surgery on Tuesday.
Hartley has not played since Saints' win at Worcester Warriors on December 21.
He has been able to do some light training with England but not featured in the Six Nations.
And he is now likely to be sidelined for at least four weeks, according to Saints boss Chris Boyd.
"Dylan went to see the surgeon and they felt in conjunction with our medical people the progress was a bit slow," Boyd said.
"He's going to have a surgical proceedure on Tuesday to open it up and see what's causing the knee to be grumbly.
"Depending on what they find, it will depend on how long his rehab will be.
"If it went outstandingly well, he could be playing in four weeks but if it's something a bit more problematic it might be a bit longer.
"We won't really know what timeframe it is until they have a look and then it will depend on his rehab.
"We certainly won't be putting any pressure on him. He'll play as soon as he can."