The Germany international completed a deadline-day switch to the Premier League in a deal worth a reported €50million, with several Bernabeu stars expressing their surprise at the move.
Ozil's departure was offset by the world-record arrival of Gareth Bale, who is set for a home debut when Real meet city rivals Atletico on Saturday.
But Chelsea loanee Courtois is not convinced that the Welshman is good enough to replicate the creativity that Ozil gave to Carlo Ancelotti's side.
He told AS: "Without him, Madrid lack quality in the game.
"Ozil had tremendous vision in playing the final pass between the lines and opening up the game, although it is true that they have others."
Atletico had gone into derbies of recent years with a sense of dread, going 26 years without a win after a triumph in 1999.
However, that run was finally broken in May's Copa del Rey final as Diego Costa and Miranda struck to seal the trophy for Atletico and leave Real without silverware for the season.
"When I arrived at Atleti, all the talk was about the years we had not won a derby," he added.
"Then came the cup final win, and that relieved the pressure in the sense that we no longer speak about everything that went on before.
"Obviously there is pressure, but not as much. With Madrid, you not only want to win the three points but also to defeat a rival."
