Courtney Lawes is set to leave Northampton this summer to join Brive.
According to reports in France, the former England back row has agreed a multi-year deal at the ProD2 club, who are currently sixth in the table.
Lawes had been exploring his options with Saints unable to match his wage demands with Aix-en-Provence, Montpellier and Racing 92 believed to have shown interest.
Northampton are also losing lock Alex Moon to France. Moon, 27, who has made 115 appearances for Saints, has signed for Bayonne.
“Alex's move was announced very quickly by Bayonne, and we're disappointed our supporters will have heard the news that way,” boss Phil Dowson said. “We wanted to keep hold of Moony.”
Moon said: “It feels like now is the right time to try my hand in a different league.”
