Charles Ehrlich entered his plea to reduced charges of attempted accessory to robbery and attempted burglary.
Ehrlich is one of five men who accompanied Simpson during a confrontation in September with two sports memorabilia dealers at a casino hotel room.
He's now the fourth to take a plea deal, leaving one co-defendant, Clarence "C.J." Stewart, facing trial with Simpson beginning Sept. 8.
Simpson and Stewart have pleaded not guilty to charges of kidnapping, armed robbery and assault with a deadly weapon that could put them in prison for life if convicted.
Simpson has maintained that he was trying to retrieve personal belongings and family heirlooms, and that no guns were involved.
Simpson's lawyer, Yale Galanter, said he couldn't immediately assess the effect of Monday's plea.
"The story isn't Ehrlich taking a plea," Galanter told The Associated Press. "The story is what he says in his sworn testimony. If it's truthful, it would support Mr. Simpson's defense."
Galanter said the plea deal "shows the prosecution is stretching to try to fill holes in an otherwise weak and crumbling case."
Clark County District Attorney David Roger wouldn't comment.
Stewart's lawyer, Robert Lucherini, also declined to comment. He has said he intends to ask the Nevada Supreme Court to sever Stewart's trial from Simpson's.
Under his plea deal, Ehrlich, 54, of Miami faces a possible sentence ranging from probation to five years in prison. Clark County District Court Judge Jackie Glass said he would be sentenced after Simpson's trial.
Of the other defendants, Charles Cashmore, 41, pleaded guilty to felony accessory to robbery and could receive probation or up to five years in prison; Walter Alexander, 47, pleaded guilty to felony conspiracy to commit robbery and could face probation or up to six years in prison; and Michael McClinton, 50, pleaded guilty to robbery and conspiracy to commit robbery, felonies that combined could get him probation or up to 11 years in prison.
McClinton testified that Simpson asked him to bring guns and "look menacing" during the confrontation with the two memorabilia dealers.
Meanwhile, district court spokesman Michael Sommermeyer said the first 100 of 500 prospective jurors being summoned for the Simpson trial reported to court Monday to fill out questionnaires about their opinions, exposure to media coverage of the case, and their availability to serve during the estimated six-week trial.
Attorneys and the judge plan to meet Aug. 25 to begin eliminating those deemed biased or unable to serve on a long trial.
