"Happy to have my shoes on for the first time in a week and be walking out of the hospital! Thanks for all of the support, " Horner wrote on Twitter.
He added in later tweet: "And a HUGE thanks to @lampre_merida, the Lecco hospital doctors and nurses, and everyone in the area who helped me out after the crash!"
The 42-year-old is highly unlikely to start the Giro d'Italia on May 9 in Northern Ireland as he suffered a punctured lung in the accident along with broken ribs and a cut to his head which required stitches.
In an interview on Tuttibici, Lampre team manger Brent Copeland, who is also 42-years-old, said that Horner was certain to miss the Giro and suggested that Horner would instead ride the Tour de France in support of world champion Rui Costa.
However, Copeland added that team's immediate priority was the health of the American rather than planning his racing schedule.
Horner signed for Lampre on a one-year deal after his newly signed agent Baden Cooke made contact with the Italian team with the plan to ride the Giro and then defend his Vuelta a España title.