ESPN reported the directive is aimed at preventing Juan Nunez from having any contact with players in the wake of allegations he masterminded a scheme to set up a fake Web site meant to explain away Cabrera's positive test for banned performance-enhancing drugs.
Cabrera, who was MVP of the 2012 All-Star Game, was banned for 50 games last week after testing positive for testosterone.
Citing "an official of one team that received it," the broadcaster said the directive declares Nunez "is not certified as a player agent" and instructs teams to "not conduct contract negotiations with Nunez or otherwise deal with him regarding players on the 40-man roster."
Nunez -- a paid consultant to Cabrera's sports agents -- told the New York Daily News he has taken responsibility for a scheme in which a phony Web site was established to make it seem Cabrera's positive result had been the result using what turned out to be a fictitious dietary supplement.
The Giants were in first place in the National League West Tuesday, a half game ahead of the Los Angeles Dodgers.