Jim Mallinder has confirmed Saints will be bringing in a long-term replacement for Louis Picamoles.
But the new player will not move to Northampton until the start of the new year and has not been named by the Saints chief.
Sam Dickinson has been drafted in on a short-term deal, having originally been released at the end of last season.
“Louis Picamoles had left the club so we needed a replacement,” Mallinder said.
“We have got a long-term replacement for Louis Picamoles, but he won’t be here until the new year.
“Sam was out of contract and he’s got some things going on after Christmas but he was available on a short-term deal and it was an obvious thing to do.
“He knows the club, he’s a great leader, he’ll be pushing for a first-team spot and he’s trained really well during pre-season.
“We’re delighted he’s joined us on that short-term deal.”