Richard Sherman has insisted that he did not take banned prescription drug Adderall.
The Seattle Seahawk is facing a four-match suspension after failing a drugs test, along with teammate Brandon Browner.
The cornerback tweeted: "This issue will be resolved soon and the truth will come out. Not worried"
Both players started in the Seahawks' loss to the Miami Dolphins on Sunday.
The pair intend to appeal the findings, and can continue to play until their cases have been heard.