Big-spending Lyon were promoted to the Top 14 on Saturday as a bonus-point 31-13 defeat of Tarbes assured them the Pro D2 championship title.
Lyon, who with a budget of 15million euros have recruited the likes of former France internationals Lionel Nallet and Sebastien Chabal, last played in the Top 14 in the 2011/12 season but finished bottom and were relegated.
LOU won the old French title in 1932 and 1933 but have not been a real force since. They will be joined in the elite league by a second club, who will emerge from the play-offs contested by the second to fifth-placed teams.
The two promoted clubs will replace already relegated Biarritz and one of Oyonnax, Perpignan and Bayonne, who play their final matches of the season next weekend.