The Portuguese outfit are keen to reinforce the left side of their defence and have expressed an interest in the Swiss stopper, who is out of favour at Juventus
The Portuguese side are in the market for a new left full-back, as Emerson and Joan Capdevila both look set to leave the club this summer following disappointing maiden campaigns at the Estadio da Luz.
Ziegler, 26, signed for Juventus last year on a free transfer from Sampdoria but was soon shipped out on loan to Fenerbahce at the end of the transfer window, having been deemed surplus to requirements by coach Antonio Conte.
He is currently assessing his options as he knows that his situation at the Bianconeri is not likely to improve anytime soon, with Pablo Armero expected to join the club to prove cover for Paolo De Ceglie.
The former Tottenham man, who has 26 international caps to his name, is contracted to Juventus until 2015.