Scotland lock Alastair Kellock will miss the Six Nations after undergoing surgery on an arm injury.
Glasgow confirmed their captain would be out for about four months after injuring his arm during their Heineken Cup defeat by Cardiff at Scotstoun this month.
The 32-year-old has been a regular starter for the international team and joins fellow Glasgow and Scotland lock Jonny Gray on the sidelines.
Northampton have drafted in the Samoa full-back Fa’atoina Autagavaia as injury cover. The 25-year-old arrives under the special dispensation rule to help fill the gaps left by the absence of Ben Foden and James Wilson. Autagavaia has eight caps for Samoa.