Madrid (Spain), Sep 6 (IANS): FC Barcelona and Atletico Madrid will start their Champions League campaigns on Wednesday night with must-win home matches.

Barcelona kick off their European campaign with the pressure of knowing the club's delicate economic situation means it is vital for them to make it beyond the group stage this season after finishing third in their group last time around.

However, Xavi Hernandez's side have been given a tough group where Bayern Munich and Inter Milan will be important rivals, meaning it is vital for Barca to start with all three points at home to Czech outfit Viktoria Plzen.

Barca go into the game after scoring 10 goals in their last three La Liga matches, with Robert Lewandowski, Ousmane Dembele and Raphinha working well together in attack, while Alejandro Balde has been a revelation at left-back and Eric Garcia looks more settled in defense.

Xavi could use the match as the chance to introduce some squad rotations and the latest arrivals. Marcos Alonso and Hector Bellerin could play some part, while Frenkie de Jong has a good chance of starting in central midfield and Jordi Alba -- suddenly relegated to second or even third choice left-back, could also play.

After a difficult summer, it seems optimism has returned to Camp Nou, but Barca's debt also means there is huge pressure on them to perform in Europe.

Atletico Madrid begin their Champions League campaign with a home game against arguably their toughest rivals in the group when Porto visit the Metropolitano Stadium.

The Portuguese side are currently fifth in their domestic competition, with four wins from five games, and in a group also containing Club Brugge and Bayer Leverkusen, starting with three points would give Atletico a big advantage ahead of the remaining group games.

Atletico will be without Jan Oblak after the goalkeeper suffered a knock in their weekend draw away to Real Sociedad, meaning Ivo Grbic will be in goal on Wednesday.

Antoine Griezmann will once again start on the bench as Atletico continue with their policy of ensuring they don't have to pay Barca 40 million euros for the striker at the end of the season.

Griezmann's loan deal says Atletico will have to pay that money if Griezmann plays 45 minutes or 50 percent of Atletico's games and to avoid that, the forward has so far been used as a substitute with just 30 minutes to play in each game.