A banner hung overnight from Wednesday to Thursday on the same bridge, located not far from Real's training camp, bore the inscription "Madrid hates Real".
Spanish media have denounced the fake hanging of the 22-year-old as a 'racist attack' and a 'serious threat' against the Real Madrid striker.
Police told AFP they had opened an investigation into the incident, without providing further details.
Atlético Madrid fans have in the past used the slogan 'Madrid hates Real Madrid' against Los Blancos.
Last September, some were filmed singing racist lyrics hostile to Vinicius Jr before the championship game between the two teams.
The investigation carried out by the police at the time did not identify the authors of these racist songs.
"We have to protect him," Real manager Carlo Ancelotti commented on Vinicius at a press conference on Wednesday.
"Football needs him. He has an extraordinary talent and we have to protect him both physically and mentally."
Thursday night's match will be played at Real Madrid's Santiago Bernabeu Stadium.
© 2023 AFP