League officials did not say Thursday what substance was found in Saunders' test. He can practice with the Colts throughout training camp and will be eligible to play in preseason games. But he won't be eligible to play in the regular season until after the Colts' game Nov. 3 against Houston.
Saunders is no stranger to controversy.
Last year, the NFL imposed a four-game suspension on Saunders for violating the same substance policy. The Steelers subsequently released Saunders in October. Indianapolis signed him five days later and he wound up catching two passes for 15 yards.
He also got into trouble in college. At South Carolina, he was questioned by NCAA investigators about possible contact with an agent and was later suspended by Gamecocks coach Steve Spurrier for violations the coach said were not related to the NCAA probe. Less than a month after first announcing the suspension, in August 2010, Spurrier kicked Saunders off the team.
Instead of transferring, Saunders wound up forgoing his final year of eligibility to enter the NFL draft.
Saunders is the third Colts player in less than a month to run into trouble off the field.
In June, the league announced receiver LaVon Brazill would be suspended for four games for violating the league's substance-abuse policy. Earlier this month, backup safety Joe Lefeged was arrested in Washington on a gun possession charge. He has not been disciplined by the league.