American sprinter Sha'Carri Richardson has tested positive for cannabis, sources told Reuters on Thursday, and she is unlikely to get the chance to challenge for the Olympic 100-meter title in Tokyo later this month.

One source familiar with the matter told Reuters the positive test came at the U.S. Olympic trials last month where Richardson established herself as a gold medal contender by winning the 100 meters in 10.86 seconds.

A positive test during the trials would mean all of Richardson's results from the meet would be wiped out, voiding her victory in the 100-meter final.

Another source familiar with the matter told Reuters that Jenna Prandini, who finished fourth in the final, had already been approached to run for the U.S. in the 100 meters in Tokyo.

Both sources requested anonymity to Reuters due to the sensitivity of the matter.

Calls and e-mails by Reuters to Richardson's agent, Renaldo Nehemiah, the U.S. Anti-Doping Agency (USADA) and U.S.A Track and Field (USATF) went unanswered on Thursday.

In a cryptic tweet earlier in the day, Richardson wrote: "I am human."

The 21-year-old will appear on NBC's "Today Show" on Friday, the network confirmed to Reuters.

Richardson was billed to run in the 200 meters at the Stockholm Diamond League meeting in Sweden this weekend but she was not on the entry list for the meet's official website on Thursday.

Cannabis is banned by the World Anti-Doping Agency (WADA), but if athletes can prove that their ingestion of the substance was unrelated to sports performance then a suspension of three months rather than the usual four years is imposed.

If an athlete is willing to undertake an approved treatment program in collaboration with their national anti-doping body then the ban can be reduced to one month.

The Texan was aiming to become the first American woman to win the Olympic 100-meter title since Gail Devers in 1996 after posting 10.72 seconds in April -- one of her five runs under 11 seconds this season.

A 30-day ban backdated to the time of the adverse result could leave Richardson clear to race in the 4x100-meter relay at the Olympics on Aug. 6, if selected by USATF. There are six athletes entered into the 4x100; four are qualifiers based on their performance in the 100-meter individual race and two will be named by USATF, so Richardson could have a chance to participate.

Richardson could also appeal any sanction to the Court of Arbitration for Sport (CAS), as could any other sports body who felt a punishment was too lenient.

Information from Reuters was used in this report.