Ruggeri just turned 19 this month and is a product of the prolific Dea youth academy.
He made eight senior appearances for Atalanta last season, six in Serie A and two in the Champions League.
The left-back has joined newly-promoted Salernitana on loan with an option to buy.
However, Atalanta also retained a counter-option should they wish to bring him back to Bergamo.
He was no longer required by Gian Piero Gasperini after Atalanta signed Giuseppe Pezzella from Parma to act as alternative to Robin Gosens on the left flank.