MADRID (AP) — Scoring hasn't been a problem for Real Madrid recently, especially with Cristiano Ronaldo in top form.

But the European champions could have issues in defense when they host Juventus in the second leg of the Champions League quarterfinals on Wednesday.

Madrid will try to protect its three-goal advantage from the first leg with coach Zinedine Zidane unable to use his best players in central defense.

Madrid captain Sergio Ramos is suspended and his immediate substitute, Nacho Fernandez, is out injured. Raphael Varane just returned from injury, and the other central defender in the squad, 21-year-old Jesus Vallejo, hasn't been fully fit and it remains unclear if he will be able to make it to the match at Santiago Bernabeu Stadium.

Madrid won the first leg 3-0 in Turin, with Ronaldo scoring with a spectacular bicycle kick for his second goal of the match. Madrid can reach the semifinals for the eighth straight year even if it loses Wednesday's game by two goals.

Zidane probably would have liked not to force Varane's return in the Spanish league derby against Atletico Madrid this weekend, but he couldn't rest him because Vallejo was bothered by muscle discomfort in practice last week.

Exams showed no major injury to Vallejo, but he trained separately from the squad on Monday before joining the rest of the team on Tuesday.

"Jesus had a good practice session, he didn't feel anything," Zidane said. "Tomorrow (Wednesday) we will see who gets to play. We shouldn't have any problems. If we do, we will adapt."

Vallejo is Zidane's last option to play in central defense, and the youngster didn't impress in the few times he got to play this season. He has made only eight appearances, mostly when Zidane chose to rest his regular starters. His last match was against Las Palmas following the international break last month. Vallejo's last Spanish league match before that was against Sevilla in December.

"Jesus is a good player," Varane said. "He doesn't have experience in this competition (Champions League) but he has a lot of quality. From what we've seen in practice, he is fine. If he plays, all of us will be confident that he can get the job done."

Madrid didn't concede against Las Palmas, but before that it conceded at least once in five straight matches, including three times against Girona in a league game at home.

In the attack, Madrid has scored in seven straight matches, with Ronaldo continuing to impress. He has found the net 20 times in his last 10 games, including in the 1-1 derby against Atletico on Sunday.

The match against Juventus will be Ronaldo's 150th in the Champions League.

If Vallejo can't play, Zidane will have to improvise in central defense, likely using midfielder Casemiro to play alongside Varane. Mateo Kovacic would likely enter the lineup to replace Casemiro in the midfield, or Zidane could choose a more aggressive setup with an extra attacking midfielder such as Marco Asensio or Francisco "Isco" Alarcon.

"Casemiro is used to playing in the midfield but he has practiced in the back many times," Varane said. "We know how he defends, how he plays."

Madrid has won three Champions League titles in the last four seasons, including the last two in a row. The team defeated Juventus 4-1 in last year's final.

No team has ever overturned a 3-0 home loss in the Champions League.

"We'll need to play a complete game against a complete team if we are to get a positive result," Juventus coach Massimiliano Allegri said. "Nobody expected us to concede after two minutes in Turin, so why can't we do the same tomorrow (Wednesday)."

If Juventus can't come back, it could be the final Champions League match for veteran goalkeeper Gianluigi Buffon.

"Trying to achieve the impossible will help us achieve the possible," the 40-year-old Buffon said. "This is what we need to do. We need to play with this kind of spirit against an amazing side."

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