Barcelona's Lionel Messi, left, celebrates with Ansu Fati after scoring the opening goal during a Spanish La Liga soccer match between Barcelona and Granada at Camp Nou stadium in Barcelona, Spain, Jan 19, 2020. (JOAN MONFORT / AP)

MADRID - Spain's matchday 21 comes with both Atletico Madrid and FC Barcelona having something to prove after their performances at the start of January. Here are some things to look out for this weekend in Spain.

Valencia will be Quique Setien's toughest challenge to date and he needs his side to turn possession into chances, if that doesn't happen, his short honeymoon at the Camp Nou is likely to come to an end

1. Can Barca turn possession into chances against Valencia?

Quique Setien's first two games in charge at FC Barcelona have seen his new side show both his virtues and defects as a coach.

Setien kicked off his Barca career with a 1-0 win at home to Granada, but it escaped nobody's attention that despite his side enjoying 80 percent of the ball, they only scored in the last 20 minutes after Granada had a player sent off.

Wednesday's 2-1 Copa del Rey win in Ibiza followed a first half in which they again had 80 percent of the ball, but failed to produce a single shot on target against a third-tier rival that not only scored, but also hit the post and had a goal ruled out.

ALSO READ: Atletico knocked out of Cup at third-division Leonesa

Valencia will be Setien's toughest challenge to date and he needs his side to turn possession into chances, if that doesn't happen, his short honeymoon at the Camp Nou is likely to come to an end.

2. The pressure is on Simeone

If Barca has failed to convince under Setien, it has been an even worse week for Atletico Madrid under Diego Simeone. Last Saturday's 2-0 defeat in Eibar virtually ended Atletico's options in the Liga Santander as his side again failed to create enough chances to take anything from the game.

Things went from bad to worse on Thursday when they crashed out of the Copa del Rey after a humiliating 2-1 defeat away to third-tier Cultural Leonesa and Simeone is facing the strongest criticism since he took over at the club at the end of 2012.

This weekend sees Atletico face struggling Leganes and with a visit to play Real Madrid on the horizon, it's vital his side react, but with no Cup and the league looking impossible, Simeone is going to need all his motivational skills.

Real Madrid's Casemiro scores his side's opening goal during the Spanish La Liga soccer match between Real Madrid and Sevilla at Santiago Bernabeu stadium in Madrid, Jan 18, 2020. (MANU FERNANDEZ / AP)

3. Crunch time for Espanyol

Although Espanyol was knocked out of the Copa del Rey in midweek after fielding a side of fringe players away to Real Sociedad, coach Abelardo Fernandez has returned hope to the club with a draw at home to FC Barcelona and a win away to Villarreal in his first two league games in charge.

The club has also shown it is willing to spend money to escape the relegation zone with the signings of Raul de Tomas, Adrian Embarba and Leandro Cabrera at a total cost of around 40 million euros (around 45 million euros) since the start of the month.

Saturday's rivals Athletic Club Bilbao travel after playing 120 minutes in the Cup with a strong side on Wednesday and Espanyol will hope to take advantage of some tired legs to take three more vital points.

READ MORE: No big surprises but favorites all suffer in Copa del Rey

4. Celta also need something special

Thursday night could hardly have gone worse for Celta Vigo, who were knocked out of the Copa del Rey after playing a leg-sapping 120 minutes away to second-tier Mirandes in a game which also saw them lose influential playmaker Rafinha with a straight red card.

Coach Oscar Garcia needs his side to recover and react ahead of Sunday's league game at home to Eibar, who will also be looking to bounce back after crashing out of the Cup to lower league rivals.

Last Saturday saw Celta play some good football as they took a 1-1 draw in Bilbao, but with 16 points from 20 games, they need their points to add up three at a time.