Real Madrid's miserable run of results continued as they slid to a shock 1-0 La Liga defeat at Alaves and failed to score in a fourth-straight game.
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Barcelona began the new La Liga campaign with a 3-0 win over Alaves on Saturday with the help of a spectacular under-the-wall free kick from Messi.
The Ghana international signed a four-year deal with the Spanish side on Monday.
Morocco's football federation has lost its case against FIFA to recruit Spain forward Munir El Haddadi before the World Cup.
Atletico Madrid stayed mathematically in the La Liga title race, for a few hours at least, with a 1-0 victory over Alaves.
Alvaro Medran, on loan from Valencia, showed his frustration over his lack of playing time at Alaves by crying during a postgame interview.
Morocco's hopes of adding Munir El Haddadi to their World Cup squad have been dashed by FIFA.
Simone Zaza scored one goal and set up another for Rodrigo Moreno as Valencia claimed a 3-1 La Liga win over Alaves at the Mestalla Stadium.
Cristiano Ronaldo scored twice to lead Real Madrid to a 4-0 rout of Alaves at the Bernabeu on Saturday.
Katai, 27, has not started a game this season for Alaves and has made only four substitute appearances in all competitions.
Alaves defender Victor Laguardia suggested his side were denied a last-minute penalty at Camp Nou
Barcelona needed a second-half rally to overcome Alaves 2-1 and maintain their unbeaten run in La Liga on Sunday.
Alaves continued their upturn in fortunes under new boss Abelardo Fernandez to beat struggling Las Palmas 2-0.
La Liga side Alaves have sacked Gianni De Biasi just over two months after appointing him and are searching for their third head coach of the season.
Barcelona forward Munir El Haddadi is hopeful that FIFA will grant him clearance to represent Morocco at the 2018 World Cup.
Dani Ceballos fired a La Liga debut double to ease pressure on boss Zinedine Zidane as Real Madrid edged out Alaves 2-1.