McKennie made 29 appearances for Juventus in all competitions last season, scoring four goals. He has also become a key figure for the United States, with nine goals in 35 international appearances.
Juventus lost another option in midfield when Aaron Ramsey terminated his contract by mutual consent last month.
Massimiliano Allegri's side are looking to win Serie A for the first time since 2020, having finished fourth in each of the last two seasons. They lost their latest preseason friendly 2-0 against Real Madrid.