Munoz became Andoni Iraola's first Liverpool signing after his move was completed on Thursday, as confirmed by the club, who were keen on replacing Mohamed Salah, who will leave the side this summer.
The 19-year-old joins from Osasuna after Liverpool triggered his £34.5 million release clause as he dodged a move to Premier League rivals Newcastle, who had been scouting the winger for a number of months.
Having scored seven goals and laid on five assists in 36 games for Osasuna following his €6 million move from Real Madrid last summer, the teenager clearly impressed Liverpool, who see him as a player who can slot straight into the side.
However, as reported by the Liverpool Echo, Munoz has aggravated a muscle problem that he picked up in the lead-up to the World Cup, hurting his chances of featuring for Spain at the tournament.
Munoz, who made his international debut in March, can play on both wings and has signed a six-year deal at Anfield.
His injury setback will be a worry for fans who endured long-term injuries to the likes of Alexander Isak, Hugo Ekitike and Jeremie Frimpong last season.
The winger underwent a medical in Chattanooga before the move to Merseyside was confirmed, but this injury is said to have been picked up after he put pen to paper.
A statement on Munoz from the Royal Spanish Football Federation (RFEF) medical team said:
"During the planned and individualised recovery process, an additional muscle injury has occurred that will delay his return to competition. His availability for the upcoming matches will depend on the evolution of his symptoms."