Highly rated shortstop prospect Delvin Perez tested positive for an unnamed performance-enhancing drug in advance of this week's Major League Baseball draft, according to multiple sources.

Perez has been sliding down some draft boards because of the failed drug test, which was first reported by Jon Heyman of Today's Knuckleball.

Perez is a 17-year-old shortstop from Puerto Rico who was originally projected as a top-5 pick in this year's MLB Rule 4 draft, which begins Thursday night at 7 ET. He was ranked No. 3 on the latest Big Board of the top 100 draft prospects, which was published prior to the revelation of the positive test.

Sources said that teams first began learning of Perez's positive test last week, and he may no longer go at the top of the draft.

MLB tests the top 200 draft prospects each year for various performance-enhancing drugs and drugs of abuse and reports the results to club officials who inquire about specific players. A positive test does not affect a player's eligibility for the draft.

Dan Halem of Major League Baseball declined to comment, citing the league's agreement with the Players Association that they "do not publicize drug testing results of prospects because they are amateur players until they sign a professional contract. The program itself which is sent to the prospects states that their results will remain confidential."

Previous high picks who tested positive include current Colorado Rockies pitcher Jonathan Gray, who tested positive for the stimulant Adderall in 2013 but was still selected third overall by Colorado.