Roger Clemens' chief accuser is expected to testify against the former pitcher. It will be a make-or-break moment for the prosecution as it seeks to convict Clemens of perjury.
Brian McNamee, Clemens' former strength coach, takes the stand Monday as the trial moves into its fifth week. McNamee says he injected the seven-time Cy Young Award winner with steroids and human growth hormone in 1998, 2000 and 2001.
Clemens is accused of lying to Congress when he denied using those drugs.