The fullback moved to Stuttgart on-loan in January.
"I do not think there are anymore doubts," agent Pasquale Gallo told calciomercato.it. "Stuttgart has already expressed they want to keep him. I've talked to the Germans, their desire is to re-sign him and Cristian is enthusiastic about this experience.
"Coach (Christian) Gross rates him and vice versa, the Swiss is a transparent person and honest."