The Frenchman, 36, was released by the Pilgrims at the end of last season after making more than 100 appearances during his 30-month stay at Home Park.
Nalis played for Le Havre, Caen, Guingamp and Bastia in his homeland, as well as Italian side Chievo before arriving in England with Leicester City five years ago.
He also had a brief spell with Sheffield United before joining Plymouth in January 2006.