Real Madrid forward Gareth Bale was jeered by supporters during a sponsorship event in the Spanish capital on Friday afternoon.
The 28-year-old, booed inside the Bernabeu in each of Los Blancos' last two home games, was carrying out promotional duties for adidas when targeted by disgruntled fans.
Bale has been accused of playing below par since returning from injury at the tail end of last season, while AS reports that some in the crowd yelled "speak Spanish".
Casemiro has backed Bale to respond to his critics by helping Madrid to more silverware this season.