Alexander-Arnold is set to face his boyhood club for the first time since leaving the club on a free transfer, with the pre-match hostility already simmering.
The mural, which commemorates the defender's part in Liverpool's 2019 Champions League triumph, was targeted with white paint by vandals early on Tuesday.
The words "Rat not welcome" and "Adios el rata" (Goodbye, rat) were scribbled right across the artwork, which is on the side of a house close to the stadium.
Workers were seen removing the paint from the mural by midday.
The act suggests Alexander-Arnold may want to brace for a hostile reception at Anfield when Real Madrid and Liverpool clash this evening.
The 27-year-old's choice to leave the club angered supporters and he was booed in his first match since making the announcement in May.
His mural features his quote: "I'm just a normal lad from Liverpool whose dream has just come true", after the Reds' victory in Madrid.
It was commissioned by The Anfield Rap podcast and includes the name of the food poverty charity Fans Supporting Foodbanks.