U.S. District Judge Reggie Walton told lawyers Tuesday that the juror won't be able to return following the death of her mother last week. The juror works in law enforcement with the local public transportation authority in Washington, D.C.
Two jurors previously were dismissed for sleeping.
Clemens, a seven-time Cy Young Award winner, is accused of lying to Congress in 2008 when he denied using steroids or human growth hormone.
Clemens' lawyers say they will need seven or eight court days to put on their defence, which is expected to start Tuesday.