The 20-year-old winger's contract with the Reds expires this summer and he's understood to have agreed a four-year deal with the Serie A outfit.
“Four years ago when I arrived at Liverpool I was still a child. Now I leave as a man and I take with me a new family which I'll feel is mine forever," he posted on social media.
“It's not easy finding the right words for thanking everything Liverpool FC has given to me these years.
“To every coach I had in Academy and Melwood, to every team-mate I shared good moments with, to every employee who was always by my side, thanks a lot.
“I don't know how or when but I'm sure we'll meet again someday. Stand by with me on June 1. I'll be one more helping the team to win the Champions League final. #YNWA."