By Iain Rogers
MADRID, Nov 6 (Reuters) - Real Madrid have spent several hundred million euros assembling one of soccer's most lethal attacking units, but coach Carlo Ancelotti is still tinkering with a defence that again looked shaky in Tuesday's Champions League draw at Juventus.
With Portugal forward Cristiano Ronaldo and Wales winger Gareth Bale playing either side of France striker Karim Benzema in a three-man attack, Real are almost impossible to keep at bay, especially with Ronaldo in such prolific form.
However, they have a less impressive record at the back, where they have managed to prevent their opponents scoring only twice in 12 La Liga outings this season, and once in four games in Europe's elite club competition.
In the 2-2 stalemate in Turin, when Ronaldo netted his eighth goal in Europe this term and record signing Bale opened his Champions League account for his new club, Real conceded a fifth penalty in their last three outings in all competitions.
Building a team on the assumption you will always score more than the other side is a precarious foundation on which to mount a challenge for a 10th continental crown and first since 2002.
"We are the first to know that we can give a lot more," goalkeeper and captain Iker Casillas told reporters.
"We have shipped goals in the last few games but we are working really hard on defence," added the Spain international.
"With our quality we are going to create chances and if we manage to keep a clean sheet we are practically assured of three points."
Ancelotti, in his first season in charge after taking over from Jose Mourinho, opted not to use either of his recognised rights backs Alvaro Arbeloa and Dani Carvajal against the Italian champions, instead switching Sergio Ramos over from centre back.
Pepe, who has looked nowhere near his imperious best this season, and Raphael Varane played in the middle of the defence, with Marcelo on the left, and it was the inexperienced Varane who gave away the penalty and was at fault for Fernando Llorente's equaliser.
Ancelotti justified his defensive formation by saying he wanted more power in the air.
"Carvajal and Arbeloa were available but in Madrid Juventus played a lot of balls to the far post and we had problems," the Italian told a news conference.
"Ramos is very good at heading and that's why he played there (at right back).
"He did well, he is a centre back but when the team needs it he can play there, it's a temporary thing. We were more comfortable with the crosses."
Real's point in Turin, which followed their 2-1 win at home to Juve last month, leaves them on the brink of qualification for the last 16 with 10 points from four of six matches.
Galatasaray and FC Copenhagen each have four points with winless Juve bottom of the group on three. Real host Galatasaray on Nov. 27, when Juve are at home to Copenhagen. (Editing by Patrick Johnston)