Jonathan Gray, the University of Oklahoma pitcher and No. 2 prospect heading into this year's MLB Rule 4 draft, tested positive for the medication Adderall during baseball's predraft drug testing program, according to multiple sources familiar with the details of Gray's test.

The positive test will not result in a suspension, but will make Gray subject to additional follow-up testing once he begins his pro career, according to a source with Major League Baseball. Adderall comprises salts of two amphetamines and is banned by MLB unless the player has a valid therapeutic use exemption. Multiple sources indicated that Gray did not have a prescription for the drug.

A message asking Gray for comment was not returned.

Gray, a 6-foot-4, 239-pound junior from Chandler, Okla., is likely to be one of the first five players taken in Thursday's Rule 4 draft. One source told ESPN.com that he did not think Gray's failed test would harm his draft stock.

Jonathan Gray remains projected as a top-five pick. Andrew Woolley/Four Seam Images/AP Images

Adderall use without an exemption is prohibited under the Joint Drug Agreement between Major League Baseball and its players' union. More than 110 players were granted exemptions in 2012, according to the independent program administrator's report released in November. Philadelphia Phillies catcher Carlos Ruiz was suspended for the first 25 games of the 2013 season after he tested positive for Adderall for the second time without a valid exemption.

Gray spent his freshman season at Eastern Oklahoma State College, after which he transferred to Oklahoma. He previously was drafted by Kansas City in the 13th round in 2010 and by the New York Yankees in the 10th round in 2011. He ranks second among Division I starters in strikeouts this season with 138, and takes a 1.59 ERA in 119 innings into this weekend's playoff super-regional against LSU in Baton Rouge, La. He pitched once in the Blacksburg regional, throwing a complete game against Coastal Carolina, striking out 11 in a 7-3 Oklahoma victory.

"All University of Oklahoma student-athletes are subject to institutional and NCAA drug testing and are subject to corrective action relative to those policies," the OU athletic departement said in a statement. "At this time, we are able to confirm that Jonathan Gray is eligible to compete for the University of Oklahoma baseball program."

Major League Baseball's Rule 4 draft begins Thursday at 7 p.m. ET. The Houston Astros have the first overall pick for the second year in a row, followed by the Chicago Cubs and Colorado Rockies.