One of the toughest UEFA Champions League matchups will be the one between Manchester City and Barcelona. What do the Citizens have to do to beat Los Blaugranas?

After their heart-breaking loss to Barcelona in the UEFA Champions League's Round of 16 last year, Manchester City are desperate to get some payback. Considering Barcelona has shown magnificient form this season under coach Luis Enrique, Manuel Pellegrini's men will have to play their best game in order to upset the heavily-favoured Blaugranas. The Sky Blues will not have Yaya Toure available for this match, but their hopes may be set on these key elements that we mention below.

1. Sergio Aguero's form

The Argentinian striker has been a major asset for the Citizens during his years with the club. Most of their chances lie on what he's able to do against a defense which usually struggles defending quick players such as him. Being fully recovered of a knee injury that left him off the pitch for almost two months, "El Kun" has returned in style to Pellegrini's starting XI, boosting their chances for success if he's healthy. Agüero has scored three goals since coming back to play, and his contribution will be key for his team's survival.

Aguero is tied with Diego Costa as the top goalscorers in the English Premier League

2. City's focus on the competition

After being eliminated of the FA Cup and the Capital One Cup, Pellegrini's footballers have less games in their bag compared to Barcelona's crew. Even with Luis Enrique's rotations, his key players have not enjoyed sufficient rest, which could backfire during the upcoming month, considering they will have to play Copa del Rey,  La Liga matches (including El Clasico) and their UCL games. In order for them to capitalize on Barcelona's form, they should keep pressing their defenders, who have shown some faults under pressure.

3. Ter Stegen's shaky performances

German goalkeeper Marc Andre Ter Stegen has been the starter for Luis Enrique's crew during this UCL season, but his performances keep raising doubts among fans and experts. During Barcelona's group stage defeat vs PSG, the former Borussia Moenchengladbach shot-stopper was responsible for at least two of the goals the team conceded, and facing more capable strikers like Edin Dzeko, Aguero or newest signing Wilfried Bony, the Blaugrana side may be up for a complicated time against one of the top scoring teams in this Champions League edition.

The German goalkeeper was set to be Barca's No. 1 option, but Claudio Bravo relegated him to the bench in La Liga.

4. Messi's form playing in English soil

Despite being one of the greatest players ever to grace a football pitch, Lionel Messi still has a hard time playing where the game was invented. After last year's performance against Pellegrini's side, Messi recorded just his second goal against an English side while playing in England, and some of his opponents like Pablo Zabaleta and Martin Demichelis could be capable enough to stop the player from Rosario. If Manchester City wants to reduce their opponent's chances of defeating them , then controlling La Pulga's skills will surely be one of the keys to their survival.

"La Pulga" has only scored twice for Los Blaugranas while playing in England.

5. City's midfield scores more than Barcelona's

Even with Touré unavailable for the first game, the Citizens have a more cooperative midfield that Los Blaugranas. When you talk about ball possession, there isn't any team in the world that can compare to Luis Enrique's men. But when it comes to scoring goals, Manchester City has one of the most prolific sides around the globe. David Silva, Samir Nasri, James Milner and Frank Lampard have scored more goals than Ivan Rakitic, Xavi, Iniesta or Busquets, giving their team more alternatives when it comes to attacking. With a formation including more midfielders than their opponent, the Sky Blues could enjoy more chances than their opponents on the long run, if they keep the recent form shown in the Premier League.