The attacker is presently tied to the Rossoblu until June 2015, but there are talks talking place regarding a new improved contract until 2016.
The 25-year-old caught the eye for Cagliari last season following his return from a loan spell at Juve Stabia.
Sau, who grew up in the Cagliari youth ranks, scored 12 goals in 30 top-flight games for the outfit last season.
His form was good enough to win international recognition as he was given his Italy debut in the May friendly win over San Marino.
Sau is believed to currently be on just €200,000 a season (£172,000)