The Spanish capital giants have already dropped four points in the 2017-18 La Liga season, with some critics claiming that the lack of a 'number nine' is proving costly.
"It's true that when you look at the players you had, like [Alvaro] Morata and Mariano, and when you see that now you only have [Borja] Mayoral that you might think we lack a number nine," Zidane told reporters on Tuesday.
"That might be the case, but it wasn't possible [to bring in another]. I would have liked Morata to stay, but he wanted to play more and to leave.
"It wasn't possible to sign another player, but I really believe in [Borja] Mayoral, as he is hungry. We also have Karim [Benzema] and Gareth [Bale]. We will get by with all of the players that we have."
Real get the defence of their Champions League trophy underway on Wednesday against APOEL at the Bernabeu.