Barcelona, Oct 19 (IANS): Ronald Koeman's FC Barcelona face the first of two season-defining games when they take on Dynamo Kiev in a must-win match in the Champions League on Wednesday night.

Although some sectors of the press are already looking ahead to Sunday's 'El Clasico' against Real Madrid, Barca have to give their full attention to Wednesday's game if they are to avoid an early exit from Europe.

The successive 3-0 defeats to Bayern Munich and Benfica in their first two group games mean that Barca have to win both of their matches against the Ukrainian side to have a chance of reaching the knockout stages -- something that is vital not just for the club's sporting prestige, but also for its cash-strapped finances.

Barcelona got off to a good start to the week when they beat Valencia 3-1 on Sunday night, with Ansu Fati making a huge impact on his return from injury.

Barca coach Koeman, already under pressure as his team lurches from one debacle to another, replaced the 18-year-old after an hour and Fati is certain to start on Wednesday, with Memphis Depay alongside him in the attack.

Koeman will have to make adjustments in defense, however, where an injury to Ronald Araujo and Eric Garcia's suspension after he was sent off in Lisbon means that either Samuel Umtiti or Clement Lenglet will partner Gerard Pique at the heart of the Barca defense.

The Dutchman clearly has no faith in either of the two players, but it is Lenglet, who has one appearance this season, who is likely to get the nod, while Jordi Alba and Sergi Roberto continue as full-backs, reports Xinhua.

Koeman is still without the injured Pedri, Ousmane Dembele, and Martin Braithwaite, but will have Sergio Aguero on the bench after the Argentinian's long-awaited debut in the closing minutes of Sunday's win.

Two more Spanish sides are in Champions League action on Wednesday night with Villarreal needing to bounce back from their first La Liga defeat of the campaign in their visit to Young Boys in Switzerland.

Villarreal are currently bottom of their group and need at least a point to avoid being cut off from the top.

Meanwhile, Sevilla travel to Lille in a tight Group G, where they have two draws from their first two matches in the Group stage.

In other matches, Manchester United host Italian club Atalanta, Juventus visit Zenit Saint Petersburg, Bayern Munich visit Benfica, defending champions Chelsea host Swedish club Malmo, and RB Salzburg host Wolfsburg.