The Serie A club, who agreed a new contract with coach Walter Mazzarri recently, announced the duo were to depart the San Siro on Wednesday.
Spendlhofer moves to Sturm Graz on a loan deal, with the Austrian Bundesliga club having an option to sign the 21-year-old.
Benedetti has spent the last three seasons on loan at various clubs as he too has struggled to become a regular at San Siro.
Having represented Italy at various levels, Benedetti moves to Cagliari on the same day the Sardinian club announced the signing of fellow defender Antonio Balzano.
Benedetti's Inter team-mate, Samuele Longo, has also moved to the Stadio Is Arenas on loan for the coming campaign.
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