Juventus are also in the running for Fiorentina midfielder Milan Badelj, opening up a bidding war with Milan, Inter, Atletico Madrid and Chelsea.
The Croatia international declared he would not be extending his contract in Florence, so could leave in January or at the end of the season.
His agent confirmed Milan are the preferred option due to the presence of ex-Viola Coach Vincenzo Montella.
According to Calciomercato.it, now Juventus have also joined the fray and approached Fiorentina to enquire about his availability.
The Bianconeri need a midfield reinforcement and Zenit seem unwilling to release Axel Witsel during the January transfer window, even if that means losing him as a free agent next summer.