Stubblefield was the first football player charged in the Bay Area Laboratory Cooperative steroids scandal, the San Francisco Chronicle said.
The 37-year-old Stubblefield was a defensive lineman for the San Francisco 49ers, Washington Redskins and Oakland Raiders. He retired in 2003.
Stubblefield told a federal judge he made false statements to an Internal Revenue Service agent in 2003 regarding the use of steroids.
Three days after the ex-player told the agent he had not used substances from BALCO, it was reported that he had tested positive for THG, a performance-enhancing drug sold by the laboratory, the report said.
U.S. District Judge Susan Illston set Stubblefield's sentencing for April 25. Prosecutors recommended a sentence of zero to six months, the Chronicle said.
Baseball star Barry Bonds, another athlete involved in the BALCO scandal, has been charged with perjury for testifying in 2003 that he never knowingly used steroids.