Blake Griffin has officially withdrawn from the Olympics and Anthony Davis has been added to the U.S. basketball team's roster.Griffin needs surgery to repair torn cartilage in his left knee and joins a lengthy list of American stars sidelined this summer.Davis replaced him in the Americans' 113-59 exhibition victory over the Dominican Republic on Thursday in Las Vegas, scoring nine points in the fourth quarter. The No.1 overall draft pick couldn't be put on the 12-man roster for London until Griffin had withdrawn Friday.Davis sprained his ankle during a workout with the New Orleans Hornets and was unable to scrimmage when the Americans opened training camp last Friday, ruining any chance he had of making the original 12-man roster. But USA Basketball head Jerry Colangelo asked the 6-foot-10 forward to stick around with the select team of young players that was training against the national team, knowing he could be called upon as a replacement if there were another injury.The college player of the year at national champion Kentucky last season brings rebounding and shot blocking to a team that has lost Griffin, Dwight Howard and Chris Bosh from its frontcourt.Davis will become just the third player to suit up for the U.S. in the Olympics without playing in the pros since NBA players were first used in 1992, joining the Dream Team's Christian Laettner and former Connecticut center Emeka Okafor in 2004. He will be back on the court with the Americans when they have their first practice today.U.S. sprinter fails testRelay sprinter Debbie Dunn has withdrawn from the U.S. Olympic team after testing positive for excessive testosterone.Dunn, who finished fourth in the 400 meters at Olympic trials, was selected for the American relay pool. She is the 2010 world indoor champion at 400 meters.In a statement, she acknowledged a positive doping test and said she was withdrawing from the Olympics while the U.S. Anti-Doping Agency resolves the case.USADA CEO Travis Tygart said the agency is analyzing Dunn's 'B' sample, and that "USADA appreciates Ms. Dunn voluntarily removing herself" from the team while the case is pending. No replacement was immediately named. USA Track and Field CEO Max Siegel said Dunn did the appropriate thing by withdrawing.Briefly Women's basketball: Phoenix Mercury star Diana Taurasi is healthy again and raring to go. She has missed the last 16 WNBA games with a hip flexor and ankle injury, but says she is ready for the Olympics. Hall of Fame: The 2004 U.S. Olympic Softball Team and three-time gold medalist Lisa Fernandez have been inducted into the U.S. Olympic Hall of Fame. The 2004 Olympic Team went 9-0 in Athens, a record that included eight consecutive shutouts and four run-rule victories. Fernandez won gold medals in the 1996, 2000 and 2004 games and is the only pitcher to appear in three Olympic finales.