The FBI launched an investigation after the rope was discovered in Wallace's garage stall at the Talladega Superspeedway in Alabama on Sunday (June 21).

It concluded that no federal crime had been committed as the noose had been in the garage for months.

"The FBI learned that garage number four, where the noose was found, was assigned to Bubba Wallace last week," an FBI statement said.

"The investigation also revealed evidence, including authentic video confirmed by NASCAR, that the noose found in garage number four was in that garage as early as October 2019.  

"Although the noose is now known to have been in garage number four in 2019, nobody could have known Mr. Wallace would be assigned to garage number four last week."

It had been thought that Wallace had been subjected to a racial attack, just two weeks after he successfully pushed for the NASCAR series to ban Confederate flags from its racetracks.

Wallace, the only black driver in the top series, had forced the move in the wake of protests across the United States and beyond following the police killing of unarmed black man George Floyd.

The ban faced opposition, however, and there were vehicles waving the flag, which has pro-slavery roots, outside the Talladega circuit as Wallace competed. 

The 26-year-old reportedly did not see the noose in his garage and a member of his team first noticing it before reporting it to NASCAR.

Despite the FBI's findings, Wallace suggested it did not matter when the noose had been placed in the garage. 

"It was a noose," he said, as reported by CNN.

"Whether it was tied in 2019... it is a noose."

A noose symbolises the lynching of African-Americans, a weapon of racial terrorism infamously used in the United States - particularly the south - in the 1800s and 1900s.

Some lynchings still occurred even during the civil rights movements of the 1950s and 1960s. 

Wallace is only one of eight black drivers to have started at least one race in the NASCAR Cup Series since Wendell Scott's debut in 1961.