Brazilian centre-back Willyan, 25, has been one of the best defenders in Portugal’s Liga NOS recently.
Head coach Paulo Sergio has also used Willyan as a defensive midfielder to good effect.
The towering figure was not even a regular for Portimonense in the first part of the season, but has started all but one game since the restart.
According to O JOGO, Russian giants Zenit have informed Portimonense that they want to sign Willyan.
Portimonense instantly responded by setting a starting point of €20m for negotiations.
Willyan has a €40m release clause and is under contract at the Algarve club until 2023.
A relative unknown until recently, Willyan played in Portugal’s second tier for Cova Piedade before his move to Portimonense last year.
His high-level performances have led to Zenit declaring a serious interest in adding him to their title-winning team.