US President Trump said.
The noose discovery was made shortly after Wallace had successfully campaigned for a ban on flying the controversial Confederate flag at NASCAR, a popular sport with conservative Americans.
Trump added in his tweet that the ban and the noose controversy had "caused lowest ratings EVER!"
The president's remarks came after two divisive Independence Day weekend speeches which critics said were an attempt to exploit racial animus and stoke fear among his base of white supporters, four months ahead of the presidential election.
Last week Trump, who is trailing presumptive Democratic challenger Joe Biden in the polls, shared a video of his supporters chanting "white power" - before deleting it amid an outcry.
NASCAR president Steve Phelps noted after the inquiry had finished that "the noose was real" and "our initial reaction was to protect our driver."
"In hindsight, I should have used the word 'alleged' in our statement," said Phelps.
The US has been upended by protests against racism and police brutality since the killing of African American George Floyd by Minnesota police in May.
The demonstrations have seen attacks on relics of the country's slave-holding history such as the Confederate flag and statues of Confederate generals.
Trump has branded the movement a "left-wing cultural revolution" and vowed to resist it.