Zappacosta spent the 2019/2020 season on loan with AS Roma but a knee injury in the early part of the campaign curtailed his progress.
The 28-year-old made just nine Serie A appearances during his temporary spell with Paulo Fonseca’s men last season.
Genoa survived relegation by the skin of their teeth last season, finishing in 17th place but have boosted their squad with Zappacosta’s acquisition as well as adding Juventus’ Marko Pjaca to their ranks.
Zappacosta joined Chelsea from Torino in the summer of 2017 for £22m but has largely played second fiddle to the likes of Cesar Azpilicueta and Victor Moses for a spot at right back.
He made 52 appearances in all competitions at Stamford Bridge and played 10 times in the Europa League when Chelsea won the competition last year.
The emergence of Reece James and the experience of skipper Azpilicueta has rendered Zappacosta surplus to requirement under Frank Lampard.
Zappacosta still has two years left on his Chelsea contract.
The former Atalanta man has won 13 caps for the Italian national team.
Genoa will begin their Serie A campaign this weekend when they take on newly-promoted Crotone.
