Nacho has said he does not believe Real Madrid need to sign a centre-back in the winter window, but conceded that they had been hindered by the departure of Pepe.
Pepe won the Champions League three times and captured three La Liga crowns in 10 years at the Bernabeu before leaving this summer.
And Nacho told Cadena Ser radio: "I learned a lot from him. He had a lot of experience and he left. That has been noticeable.
"But I honestly don't think we need to sign a centre-back."
Muscular problems have limited Raphael Varane to six league starts, while 20-year-old Jesus Vallejo, brought back in July after a successful loan spell at Eintracht Frankfurt, has suffered minor injuries and made just two appearances.
"We've had Varane and Vallejo affected," Nacho said. "Vallejo started against Las Palmas and did a good job. He will soon get the experience he needs.
"We have five players that can play in that position, and competition at Real Madrid is tough."
Cristiano Ronaldo recently suggested that Real needed time to adapt following the departures of Pepe, James Rodriguez and Alvaro Morata.
And Nacho said: "We all know that the team has changed with respect to last season.
"We had a more experienced side, but I don't know whether it was better or worse than the one we have now."
Real are third in La Liga, eight points adrift of leaders Barcelona after 11 games.
They play at Atletico on Nov. 18 and Nacho said: "It's a complicated game and Atletico is a top team.
"I don't think it [a defeat] would be farewell to the season, but things would become much more difficult."
Ronaldo and Karim Benzema have struggled in front of goal in La Liga, finding the target just once each so far.
But Nacho backed them and said of Benzema: "He is a worthy Real Madrid player.
"It's true that he is not the top scorer but you have to admire all the assists he provides to Cristiano or [Gareth] Bale, and in the end, he does score a lot of goals.
"He has spells, but if a striker goes a few weeks without scoring a goal he immediately gets criticised."
He said it was "normal" that Ronaldo could get annoyed, adding: "He is competitive, and when he doesn't score he gets frustrated.
"He likes to score goals and be the best and I know how he is."
Teammate Marco Asensio also praised Ronaldo, telling RTVE's Zona Mixta: "After all that he has won, the effort that Cristiano shows in every game and in every training session makes him a role model."