Judge Susan Garsh ruled that Verizon can be subpoenaed to determine the identity of the tipster who called attorney James Sultan in April, after Hernandez was convicted in the 2013 killing of Odin Lloyd.
The judge said the caller's credibility can only be determined by first learning her identity.
Sultan says the tipster called him from a blocked number and said the juror was present for a discussion about a Boston double murder Hernandez is also accused of committing.
The jurors weren't told about that case during the trial.
Prosecutors objected to the subpoena, arguing that in order to get a judge to question a juror after a verdict is returned, a defendant must show that an "extrinsic influence" may have affected the juror's impartiality.
Garsh, however, said she has not agreed at this point to a post-verdict inquiry of the juror, but only for a subpoena so Hernandez's lawyers can determine the identity of the tipster.
Sultan and a spokesman for prosecutors did not immediately return calls seeking comment Friday.
Hernandez was convicted of murder in April for the shooting death of Lloyd, a semi-professional football player who was dating the sister of his fiance. He is now serving a life sentence.
Hernandez has pleaded not guilty in the 2012 killings of two men in Boston. Prosecutors allege that Hernandez shot the men while their car was stopped at a light after becoming enraged when one of them bumped into him at a nightclub and caused him to spill his drink.Suggest a correction