Premier League champions Chelsea have been linked with a move for the 26-year-old Brazil international.
Juve signed Sandro for 26m euros (£23m) from Porto in 2015.
Chief executive Giuseppe Marotta said: "If a player decides to leave... then at the end of the day he has to go."
Sandro has won back-to-back league and cup doubles at Juventus and played in the side that lost in the Champions League final to Real Madrid.
Juve have already agreed to let right-back Dani Alves, a target for Manchester City, leave after one season in Turin.
Juventus say they have received a "substantial offer" for Alex Sandro and will not prevent the left-back from leaving the club if he wants to.