A noose has been found in the garage stall of NASCAR driver Bubba Wallace, the sport's only full-time African-American driver.
NASCAR officials say they have launched an investigation into the noose, found in Wallace's stall at the Talladega circuit in Alabama, where a race was to be held on Sunday before being postponed due to storms.
In a statement on Twitter, Wallace said: "The despicable act of racism and hatred leaves me incredibly saddened and serves as a painful reminder of how much further we have to go as a society and how persistent we must be in the fight against racism."
He added: "As my mother told me today, they are just trying to scare you. This will not break me, I will not give in nor will I back down. I will continue to proudly stand for what I believe in."
NASCAR officials have said there "is no place for racism" in the organisation.
In a statement, they said: "We are angry and outraged, and cannot state strongly enough how seriously we take this heinous act.
"We have launched an immediate investigation, and will do everything we can to identify the person(s) responsible and eliminate them from the sport.
"As we have stated unequivocally, there is no place for racism in NASCAR, and this act only strengthens our resolve to make the sport open and welcoming to all."
Two weeks ago, Wallace successfully pushed for NASCAR to ban the contentious Confederate flag at its tracks and properties amid protests against the killing of George Floyd while in police custody in Minneapolis.