The 21-year-old travelled to Turin last month to complete a medical after the clubs agreed a fee reportedly in the region of €25 million.
Massimiliano Allegri's side are now reportedly trying to sign Schick on an initial season-long loan in order to assess his progress.
However, Sampdoria owner Massimo Ferrero has slammed Juve's conduct and says they will sell the player to another interested party if the deal is not concluded.
"It's a farce," Ferrero told Secolo XIX. "He's not healthy, he's really healthy. What they found is the equivalent of a cold!
"If Juventus want to back out, we'll sell him to one of the other four clubs that are ready to buy him.
"I think he'll eventually go to Juventus. If not, we'll take him back and add a nice 'maybe', given his release clause has now expired and we can sell him for not just €30m but possibly €40-50m."
Asked about the prospect of a loan to Juve, Ferrero replied: "Sampdoria won't go back a millimetre on any agreements.
"The boy is healthy, he can play, but now we have to worry about who has put out rumours that could damage the image of one of the brightest talents in European football."