Borussia Dortmund head coach Nuri Sahin says a strong mentality will not be enough as his side need "everything" to overcome a tough test at Real Madrid on Tuesday.
Madrid won their 15th European Cup in June at Wembley as Dani Carvajal and Vinicius Junior scored late to claim a 2-0 victory over Dortmund, then managed by Edin Terzic.
Sahin has since took charge of the Bundesliga side, though he knows one of European football's most difficult challenges awaits in the Spanish capital.
"Mentality only is not enough to survive against Real Madrid, especially in this stadium, against the champions of this competition," Sahin told a press conference on Monday ahead of the Champions League clash.
"We need everything [on Tuesday]. We need a lot of quality, a lot of self-confidence, mentality of course and also, as we say in Germany, game luck.
"The game has to go our way, so only mentality will not be enough - but of course without mentality we have absolutely no chance here."
Dortmund maintained a winning start to the competition with a 7-1 thrashing of Celtic at home earlier this month after they eased to a 3-0 win at Club Brugge in their opening fixture.
Sahin's men lead the revamped Champions League standings on six points with an impressive goal difference of nine.
"It's only possible [to continue this way] as a collective against this team," Sahin added.
"The lads know what we have planned. We want to be brave and build on the last two games in the Champions League."
Sahin, who played for both clubs, will visit Bernabeu for the first time as a coach following his appointment last summer. The former Turkey midfielder was Edin Terzic's assistant manager at the club prior to that.
"[Being back] means a lot to me because it was always my dream to play one day for Real Madrid. My son was born in this beautiful city, and I have him with me [here]," Sahin said.
"Now I have the privilege to be on the sidelines with my childhood club against one of my biggest dreams, so it means a lot to me.
"Even if it was not that long that I played for Real Madrid, it will always remain special for me. Not only for footballing reasons but also family-wise, it's a fantastic thing to be here."