The US Anti-Doping Agency has withdrawn its case against sprinter Christian Coleman, the fastest man in the world this year.

Coleman, 23, had been charged with missing three drugs tests and was facing an automatic one-year ban.

Usada said it had withdrawn the charge after receiving guidance from the World Anti-Doping Agency (Wada).

Coleman is now free to compete at the World Athletics Championships, beginning in Doha on 28 September.

The American ran a world-leading time of 9.81 seconds in the Diamond League in California in June.

Why has Usada withdrawn its case?

Under the 'whereabouts' system, athletes must let officials know where they will be for one hour every day as well as details of overnight accommodation and training.

Failure to do so - a 'filing failure' - three times in a 12-month period could lead to a rule violation under the World Anti-Doping code.

Usada said clarification from Wada had been sought around the interpretation of the current International Standard for Testing and Investigations (ISTI)

This concerned the date on which a failure to update an athlete's changed whereabouts information should be considered to have occurred.

Usada recorded filing failures for Coleman on 6 June, 2018, 16 January, 2019 and 26 April, 2019.

Two of the three tests were directed by Usada, while a third was initiated by the Athletics Integrity Unit.

However, as the ISTI states that filing failures relate back to the first day of the quarter, Coleman contended that his failure to update which was discovered on 6 June, 2018, should relate back to 1 April, 2018.

When BBC Sport tried the 'whereabouts' drugs testing system

That is more than 12 months prior to Coleman's third filing failure on 26 April, 2019.

Wada clarified this fact to Usada, resulting in the charge being withdrawn.

The decision by Usada to drop the charges can still be appealed by Wada or the IAAF, athletics' governing body.

If found guilty, Coleman would have faced an automatic one-year ban and would miss the World Championships and the 2020 Olympic Games in Tokyo.

Coleman had denied the charge and, in a statement to former sprinter Ato Bolden for the NBC network last month, said: "I'm not a guy who takes any supplements at all, so I'm never concerned about taking drugs tests, at any time."

Former Great Britain 400m Olympic champion Christine Ohuruogu received a year's ban in 2006 under the 'whereabouts' system for three missed tests.

Coleman won the US National Championships in July in 9.99 seconds.

He finished second at the 2017 World Championships in London behind fellow American Justin Gatlin and has a personal best of 9.79, making him the seventh fastest man in history.

He also set a world record for the 60m when he claimed gold at the World Indoor Championships in Birmingham last year and was talked about as a new superstar sprinter in the post-Usain Bolt era.