Champions League: The big questions for the quarterfinalists

- Real Madrid v Bayern Munich preview

- Monaco vs Borussia Dortmund preview

Are unbreachable Atleti ready to take the final step?

They're not always considered in the same bracket as Bayern Munich, Real Madrid and Barcelona but Atletico Madrid have reached the last eight four years in a row and have a third final in four years in their sights. While the talents of Antoine Griezmann, Yannick Carrasco and co. should not be dismissed, Diego Simeone's team is one where the defense is the star.

The numbers are impressive and ominous for Leicester City, their opponents on Tuesday. Atleti have not lost any of their last 21 Champions League away games by more than a goal. They've kept 7 clean sheets in their 9 European games this year and conceded just 24 in 32 La Liga games. After their 1-0 first leg win in Spain, Atleti will be confident. But defender Diego Godin said his boss leaves nothing to chance.

“There’s a huge amount of tactical work, a lot of individual work, and everything is conditioned by the way we play and what each player needs physically. Barcelona won’t train like us. There are a thousand tiny details, a throw-in, a corner, a free kick from the side, every scenario,” he said.

Can Barcelona achieve the impossible. Again?

While Leicester are used to being written off, Barcelona aren't. But the Catalans pulled off a minor miracle of their own when they overturned a 4-0 first leg deficit by beating Paris St Germain 6-1 at Camp Nou in the last round. A repeat looks an enormous challenge against a Juventus side who have conceded just 2 goals in this year's competition. But, despite the flaws in the current Barca crop, their boss thinks they've got a chance of pulling it off again and overcoming a 3-0 first leg loss on Wednesday.

"We could play as many as eight forwards against Juventus," Luis Enrique said, perhaps a little tongue in cheek. "It would not be a risk because we have nothing to lose. We have always been a team known for its attacking philosophy so it will not be a problem."

Can the Old Lady break her European trophy drought?

For their opponents, further revenge will be on the cards after Barcelona beat the Italians to the trophy in the 2015 final in Berlin. That one was particularly painful for Italy's biggest side, who have lost four finals since their last triumph 21 years ago – in the same time frame they've won 11 Serie A titles since, including the last five.

Captain Giorgio Chiellini is determined his side, who may be without first leg star Paulo Dybala, won't make the same mistakes as PSG. "We need to be compact and show no fear. [Barcelona] are like sharks who scent blood and finish you off. We've got to keep them as far away from our goal as possible," he told Sky Italia.

Is this the only chance for Monaco's scintillating young side?

The principality side have been a breath of fresh air both domestically and in Europe this term, racking up 90 goals (2.8 per game) in Ligue 1 and scoring three in each of their last four Champions League games. Thomas Lemar, Bernardo Silva and Kylian Mbappe are among a host of young talents that have propelled them to the top of the French League and the verge of the semifinals.

After a 3-2 win in Dortmund that was overshadowed by the attack on the German side's bus, Monaco may never get a chance to better their runners up gong from 2004. The Porto side that beat them in the final that year was ruthlessly picked apart by Europe's big guns and rumors suggest Leonardo Jardim's men will face a similarly uphill battle to keep their key men. It may be now or never.

Can rested Real make even more history?

Despite a relatively slender lead at the top of La Liga, Zinedine Zidane felt able to rest several of his key men for Real Madrid's 3-2 win at Sporting Gijon at the weekend, including Cristiano Ronaldo, whose two goals handed Real their 2-1 first leg win over Bayern.

The Spaniards are favorites to progress on Tuesday and to extend their Champions League title record to 12. Should they do so they will become the first side to retain Europe's premier club competition since it was re-branded in 1992.