The charge was included in a superseding indictment, a common move used by federal authorities to refine the original accusations.
Lewis is accused of trying to get the cocaine with his childhood friend, Angelo Jackson. Prosecutors say that Lewis and Jackson tried to buy cocaine in Atlanta in 2000 from an undercover informant.
Both were charged in the conspiracy case in February, but at first only Jackson was charged with attempted cocaine possession. On Tuesday, the government announced both would be charged.
Lewis' lawyers called the extra charge a minor one and didn't think it would complicate their defense. Lewis has maintained his innocence.
"This is not big news for us," said Lewis' attorney Ed Garland.
In its latest indictment, the government wrote that Lewis took Jackson to a restaurant in Atlanta to introduce him to a woman he thought could get him cocaine, although the woman waiting there was an informant.
Lewis called the informant about two weeks later and asked her to sell Jackson a kilogram of cocaine, according to the indictment. Among Lewis' charges is the use of a telephone to facilitate a felony.
Lewis' trial is scheduled to begin Nov. 1 in Atlanta. The running back has said he will not let the trial distract him from the upcoming season.
"Jamal Lewis maintains his innocence to all of the charges that have been brought, and he expects a jury will reach the same conclusion," Garland said Tuesday.