The 25-year-old has made it clear that he will only say farewell to his current club for the Old Lady, and conceded he expects to have more clarity regarding his situation soon
The Colombia international is continually being linked with the Bianconeri, who have reportedly already held talks with his agent.
The clubs are reportedly still locked in negotiations over a transfer fee, meaning the saga is unlikely to be resolved soon.
"Nothing's final yet, but I will only leave Porto for Juventus. Either I continue here, or I move to Juve, but another club is not an option," Guarin said in an interview with Radio Catena Nacional.
"A decision will be made shortly. I expect to have more clarity by Thursday."
Porto are believed to have set a €13 million asking price, while Juventus are eying a six-month loan deal worth €2m, with an obligation to buy at the end of the season for €9m.