The event, also known as March Madness, is set to begin on March 18 in Indiana, but could be without three of the United States’ biggest basketball colleges.

Virginia, who beat Texas Tech to win the title in 2019, Kansas and Duke were all forced to cancel conference matches last week due to positive COVID-19 cases.

Duke have confirmed their season is over, while it is unclear whether Kansas and Virginia will be able to field teams.

The NCAA has set a deadline of Tuesday (March 16) for sides to withdraw from the 68-team competition with Ole Miss, Saint Louis, Boise State and Seton Hall understood to be in contention to replace them.

Under the NCAA rules, teams must provide seven successive days of negative test results to play in the tournament.

Kansas pulled out of their semi-final clash against Texas in the Big 12 Conference on Friday (March 12).

"While we have been fortunate to avoid this throughout the season, there are daily risks with this virus that everybody participating is trying to avoid," said Kansas head coach Bill Self in a report by Forbes.

"We have followed the daily testing and additional protocols that have been setup for us, unfortunately we caught a bad break at the wrong time."

Virginia also had to withdraw that day from their Atlantic Coast Conference (ACC) Tournament semi-final against Georgia Tech due to a positive test.

"I'm hurting for our players, especially our seniors," said Virginia coach Tony Bennett.

"I told our young men they have every reason to be disappointed, but it still very important how they choose to respond.

"We are exhausting all options to participate in the NCAA Tournament."

Duke had appeared in 24 successive NCAA Tournaments but that run is set to come to an end after registering a positive COVID-19 cases following their win over Louisville in the ACC Tournament.

"Unfortunately, after going an entire season with no positive COVID-19 tests among our men’s basketball student-athletes and coaching staff, one member of our program tested positive following Wednesday’s ACC Tournament game in Greensboro," said Kevin White, athletic director at Duke.

"After working with our medical professionals and following Duke and ACC Medical Advisory Group health, safety, and contact tracing protocols, the student-athletes on our team are now in quarantine.

"Since last March when the pandemic started, we have listened to our medical experts and always put safety at the forefront of any determinations regarding competition.

"As a result, this will end our 2020-21 season.

"We wish every team still playing college basketball good health and the very best during the next few weeks."

March Madness was scheduled to be held across 13 different sites all over the United States, but pandemic forced organisers to stage it entirely in Indiana.

Indiana Farmers Coliseum, Hinkle Fieldhouse, Bankers Life Fieldhouse and Lucas Oil Stadium will all host matches.

Last year's March Madness was cancelled because of the global health crisis, costing the NCAA $800 million (£585 million/€665 million) following the loss of ticket sales and its television and marketing rights agreements.

The NCAA is to work with local health organisations to administer COVID-19 testing at the competition, and said it is collaborating with the Marion County Health Department to establish its protocols.

It will also work with the city and state to promote "Mask Madness", a campaign promoting health and safety by practicing social distancing and wearing masks.

As part of the initiative, the NCAA will donate thousands of masks throughout the state in the build-up to the tournament.

The college basketball season started later than normal last November because of the coronavirus but games are still being regularly cancelled or postponed due to the pandemic.