Reigning European champion Chelsea will look to overturn a two-goal deficit as it visits Real Madrid, while German giants Bayern Munich would want to avoid another upset against Villarreal in their respective Champions League quarterfinals match Tuesday.
Chelsea manager Thomas Tuchel said his team needs a "fantastic script" to qualify for the semifinals.
The Blues have been destabilized by the enforced sale of the club after the British government sanctioned owner Roman Abramovich for his close links to Russian President Vladimir Putin following the invasion of Ukraine.
Chelsea's 3-1 defeat in the first leg at Stamford Bridge last week followed a surprise 4-1 home defeat to Brentford in the Premier League, although Chelsea got back on track with a 6-0 thrashing of Southampton this weekend.
"It is one of the biggest challenges to perform away at the Bernabeu," Tuchel said.
"It is even more difficult if you have to earn a certain result, if you need to win with a minimum of two goals or better or maybe a three-goal difference, that makes it almost impossible and very, very difficult but still it is worth trying.
"We need nothing else than a fantastic script if we want to overcome this," the German said.
"The task is incredibly high and the challenge is incredibly high given the circumstances of the first leg and where we play and against whom we play and at what stage we play this kind of match.
"It's always allowed to dream and it is sometimes important to imagine things and to dream about it but it will not shift the focus from the fact that we need to deliver and we need to be ready tomorrow."
Tuchel said he believed Chelsea faces a "huge disadvantage" as 13-time European champion Real has been able to make five substitutions throughout its domestic season.
He said he believes that difference was one of the reasons his players failed to show the physical edge to their game in the first leg when Karim Benzema dominated the Chelsea defense to score his second hat trick of this season's competition.
"We face a huge disadvantage in terms of physicality because Real Madrid has a whole year with five changes and we play the most demanding league, we play the most matches throughout the season and throughout 2022 so it is not always easy to play a physical game," Tuchel said.
"We are a team that needs the physicality, the sharpness, the commitment and the investment to be a special team. We could not implement that enough in the last match."
Five substitutions will be allowed in the Premier League from next season, something which was initially put in place following the return to action after the delays caused by the coronavirus pandemic.
"We've beaten one of the best teams in the world," said captain Dani Parejo after Villarreal secured a 1-0 victory over Bayern Munich in the first leg of the Champions League quarterfinal last week. But he knows it might not be enough.
Villarreal enjoyed one of the finest nights in the club's history with a superb performance at La Ceramica that caught the six-time European champion cold.
Unai Emery's side will take a one-goal lead into Tuesday's second leg in Germany, yet the overriding feeling was regret as a series of missed chances kept Bayern alive.
"We produced a tremendous performance and if we're honest we should have won by more," said Villarreal midfielder Giovani Lo Celso.
Instead, a one-goal deficit is far from insurmountable for a team that has scored 17 goals in their last five games at home and 20 in their last four European matches at the Allianz Arena.
Villarreal has made a habit of neutralizing glamorous opponents, even if their La Liga position of seventh shows they can struggle against modest opposition.
While Emery's forensic analysis and in-depth video sessions might stifle the spontaneity needed to beat limited sides, it means his team is tactically astute and difficult to break down.
In the past year, Villarreal has beaten the Europa League champion, the Coppa Italia winner, the Bundesliga champion and the FA Cup winner. It also defeated Manchester United to win last season's Europa League.
In Spain, it is unbeaten this season against defending champion Atletico Madrid and leader Real Madrid.
After the stunning 3-0 victory in Turin that knocked out Juventus in the last 16, Villarreal will believe it can complete the job in Germany and reach the club's first Champions League semifinal since 2006.
Win or lose in Munich, the win against Bayern in the home leg will go down in the Villarreal history books.
While Bayern was winning a third consecutive European Cup in 1976, Villarreal was being relegated to the fourth tier in Spain. When Bayern won their fifth in 2013, Villarreal had just been promoted back to the top flight.
The population of Vila-real, at just over 50,000, could fit inside Bayern's stadium with 25,000 seats to spare. No smaller town has produced a team to win a European title.
For the majority of its history, Villarreal lay in the third division until Spanish billionaire Fernando Roig took over in 1998.
Roig has improved the stadium, the training ground and the team. Villarreal signed players such as Riquelme, Diego Forlan, Marcos Senna and Santi Cazorla.
They have been a fixture in the top flight for all but one of the 22 seasons this century.
With stability secured, Emery was hired to take the team to the next level, the challenge for trophies and La Liga's top four.
It has disappointed in the league but cup success has kept Emery's stock high. He was tempted by the Newcastle job in November but turned it down, the prospect of a European run too tantalizing.
Similar reasoning kept local-born star defender Pau Torres at the club he joined as a five-year-old, despite interest last summer from Tottenham Hotspur and Manchester United.
The only question now is whether the momentous win over Bayern Munich will be remembered as the pinnacle of an incredible run or the basis for something more.
"Tuesday will be the biggest challenge of my career as coach," Emery said. "And for the club as well, for the players, for lots of people here."
