Frei, 18, has joined Cardiff on an emergency one-month loan.
Frei is expected to be in the Cardiff squad for their clash with Burnley.
The Turkish teenager said: "This is a really good opportunity for me and I want to help the team achieve success.
"The move happened really quickly, everything seemed to be done in a day or so between Cardiff and Fulham.
"I can't wait to get started. I'm the sort of player who will take defenders on and look to create for team-mates around me."