Barry Bonds has found himself at the centre of a new drugs controversy after the New York Daily News claimed he had failed a test for amphetamines.
Bonds' achievements have been overshadowed by doping allegations
The San Francisco star is already being investigated for his part in the Balco steroids scandal. He has always denied knowing using banned substances.
Major League Baseball and Bonds' agent Jeff Boris have refused to comment.
Under MLB rules, players who fail one test for amphetamines are not named but must accept counselling and more tests.
A second positive test results sees the player named and handed a 25-game ban.
Bonds, 42, who has agreed in principle a new one-year deal with the Giants, is 21 home runs short of Hank Aaron's all-time record.
But his achievements have been tainted by his association with the Balco case in which his personal trainer was convicted of distributing illegal steroids.
A federal grand jury is investigating whether Bonds perjured himself when he testified in 2003 that he never knowingly used performance-enhancing drugs.
After missing all but 14 games in 2005 following three operations on his right knee, Bonds batted .270 with 26 homers and 77 RBIs in 367 at-bats in 2006.
He passed Babe Ruth to move into second place on the career home run list on 28 May.