Georgia outside linebacker/defensive end Justin Houston and Iowa defensive lineman Christian Ballard tested positive for marijuana at February's NFL Scouting Combine, multiple sources told FOXSports.com Tuesday.

Houston, an early-entry junior, is projected in some mock drafts as a late first-round draft choice at this week's NFL Draft. The 6-foot-3, 270-pound Houston had 67 tackles and 10 sacks last season for the Bulldogs as a pass-rushing linebacker.

The 6-foot-4, 283-pound Ballard was projected by some analysts to be selected as early as the second round. Ballard played at both end and tackle in 13 starts for the Hawkeyes last season, tallying 43 tackles and three sacks.

Houston and Ballard have clean police records and no known history of marijuana use.

The agents for Houston and Ballard did not return telephone calls and emails seeking comment.

The NFL Draft will take place Thursday through Saturday in New York City.