A mural celebrating Alexander-Arnold near Liverpool's stadium was defaced with the word 'rat' before the match against Real Madrid.
Fans had previously jeered the academy graduate towards the end of last season, which prompted former manager Jurgen Klopp to express his disappointment.
Manchester United legend Peter Schmeichel described the fans' treatment of Alexander-Arnold as 'disgusting', arguing he should be welcomed as a hero for his long service and trophy wins.
Former Liverpool defender Jamie Carragher disagreed, stating that fans feel 'hoodwinked' by Alexander-Arnold's departure given his past declarations of loyalty to the club.