Bellingham posted a message on Twitter and linked to a tweet that labeled the 17-year-old an "overrated talent" and concluded, "Black people only think about money."
The tweet was deleted before Bellingham posted a screenshot of it, marking the latest occasion a visible minority has been the target of racial abuse from football supporters.
A 12-year-old was arrested July 12 for sending a series of racist messages to Crystal Palace winger Wilfried Zaha. Zaha posted screenshots of abuse he received from an Instagram account belonging to a young Aston Villa supporter prior to Crystal Palace's 2-0 loss at Villa Park.
Villa condemned the actions, saying they would impose a lifetime ban for the person responsible.
Bellingham finalized a €23-million plus add-ons transfer to Dortmund on Monday, ending links between the talented midfielder and Manchester United.
Bellingham played his final match for Birmingham City on Wednesday following a decade in the organization.
The England youth international was teary-eyed at the final whistle of the 3-1 defeat to Derby County, telling the club's TV channel, "It will always have a massive place in my heart because it's my club and the club I support, and it's been a privilege."
Birmingham City expressed their gratitude for Bellingham's patronage on Thursday, retiring the No. 22 kit that "has become synonymous with Jude," according to the club.