Manchester City face an uphill mountain in the Camp Nou tonight. After a disastrous first-leg defeat at the Etihad Stadium a fortnight ago, Manuel Pellegrini and his expensively assembled squad must now stage a huge fightback against Barcelona.
It seems like an impossible job but the Catalans aren't the invincible force they once were, which definitely gives City confidence. The Spanish giants were beaten again at the weekend to make that three defeats in their last six La Liga matches.
Manchester City also suffered defeat at the weekend as they were beaten in the FA Cup by Wigan Athletic for the second time running, after losing in last season's final.
The positive news for City is that Sergio Aguero is back and will start in Barcelona. He will be an important player and Pellegrini will look to him to score the goals on his return to Spain to send City through to the quarter-finals of the Champions League.
Using statistics from Squawka, here are the three key battles to watch out for tonight.
Gerard Pique vs. Sergio Aguero
Aguero, when on the pitch this season, has been magnificent. If it wasn't for two lengthy injuries, the Argentine would have put up more of a challenge for the Premier League Golden Boot. He was right at the top with Luis Suarez and Daniel Sturridge until two injuries left him falling behind week by week. Currently, Aguero has 15 goals in 17 matches in the league and a staggering 26 goals in just 25 appearances in all competitions.
If anyone is to win the tie for City tonight, it will be the Argentine. Gerard Pique will be tasked with stopping the powerful front man, though. The Spaniard isn't as impenetrable as he once was but is still capable of keeping world class strikers quiet, should he need to. His figures in La Liga aren't fantastic, though.
Pique has won just 48 percent of his tackles (32/66) but has—rather surprisingly—won 84 headed duels. That's a huge increase on the headed duels that his opposite number, Vincent Kompany, has won.
The Belgian has won just 19 in the Premier League. It's almost as if the two figures have been mixed up between the players. Obviously, they haven't, but it just proves that Pique can battle one-on-one in the air with someone just as well as on the ground.
Pique will need to be on his toes all game though as Aguero is quick and accurate, hitting 60 percent of his shots on target in the league and 52 percent in Europe. He already has six goals in five Champions League appearances and has been lethal in European competition. The Argentine will be key for City tonight. If Pique keeps him quiet, there's most of City's chances out of the window.
Lionel Messi vs. Vincent Kompany
Lionel Messi was quiet in the first leg but managed to grab himself a goal from the penalty spot. Like Aguero, it has been an up and down season for Messi, as he's struggled with fitness while off-field financial troubles still persist.
He is back in form, though, having scored seven goals in his last six La Liga appearances. In the Champions League, Messi has been below-par by his own standards but still exquisitely dangerous with seven goals in just four games.
He has a 69 percent shot accuracy, has created six chances and Barcelona haven't lost in this season's tournament with the Argentine in the side (he didn't play against Ajax).
Vincent Kompany will have his work cut out trying to stop Messi. At the Camp Nou, Messi has played 37 games in the Champions League and scored 36 times. He's fantastic at home so Kompany cannot afford any mistakes.
In Europe, he has been close to unflappable, making 13 clearances, 10 interceptions and two blocks. He's also been a powerful tackler, winning 67 percent of the nine tackles the Belgian has contested.
He's also won his only headed duel and completed 90 percent of his passing. Kompany will need to repeat his previous performances in the tournament to stand a chance at stopping Messi. He's not yet made an error so will also be hoping to keep that statistic steady tonight.
The way things are set up, this match is destined to be decided by an Argentine.
Victor Valdes vs. Joe Hart
Now, while both goalkeepers will not directly go head-to-head, they will play an important role in tonight's match. With City chasing the game and needing to score at least two goals, Valdes is sure to be busy in goal. Meanwhile, Barcelona are dominant at the Camp Nou and test the opposition goalkeeper a lot, meaning Joe Hart will be quite busy, too.
It could be quite an open game with the English side chasing goals so both goalkeepers could be in for a hard night's work.
Valdes has played one game less than Hart in this season's competition, with the Englishman featuring in six matches. The striking difference in the two goalkeepers' figures are the number of clean sheets and goals conceded. Despite playing 90 minutes less than Hart, Valdes has kept three clean sheets—two more than Hart—and conceded just two goals. Hart has conceded 10 in City's goal but they were in a much tougher group featuring Bayern Munich.
Hart has been the busier of the two goalkeepers, it is fair to say. He's made 15 saves to Valdes' eight. However, another key difference is the number of saves made per goal conceded and the Spaniard trounces his English counterpart, averaging eight saves before conceding whereas Hart lets a goal in every 1.5 shots.
Hart will need to improve that massively for tonight's match. He has been known in the past to have fantastic performances where he saves everything but it has been a while since that happened. Maybe tonight is the night?
I think Barcelona will win this one. Messi is in fine form and, despite Kompany's obvious size and power advantage over the Argentine, he is too good to be held down for too long. The first leg of this tie was the perfect example of that.
City's best hope is to get Aguero one-on-one with Pique as his pace in the final third is electrifying. It could cause the Spaniards a lot of trouble.
Despite City's clear talent and squad depth, I just can't see Barcelona losing this tie leading 2-0, with two away goals. It is a huge ask for City, an almost impossible job.