The 18-year-old recently joined the Bluebirds on a loan deal that runs until 2 December, and has been impressed by the ambition and quality at the Welsh club.
"Straight away I can see what a good side Cardiff are. You only have to look at some of the players here," said Fulham star Frei.
"Cardiff are top of the league now and they definitely have the quality to go up and when they do, in my opinion, they will stay there."
Frei was a starlet of the Swiss national teams up the U21s, but in June chose to switch his allegiance to Turkey.