Right before the start of the NFL draft, one prospect's draft stock could be taking a hit. USC linebacker Porter Gustin failed a drug test at the combine, according to Ian Rapoport of NFL Network.

However, it doesn't seem as bad as it could've been. Rapoport reports that Gustin “was granted temporary Therapeutic Use Exemption for Adderall following the Combine.” That being said, it sounds like he was not cleared for it at the time the test was taken, so he's not 100 percent in the clear.

In a followup tweet, Rapsheet said he had viewed the documentation, and that Gustin's waiver expires on September 15th. Gustin received a lot of playing time as a true freshman, and then became a full-time starter as a sophomore. He had a breakout sophomore season and appeared setup for success at USC, but his college career was derailed by injury.

Because of various injuries, he only managed to appear in four games as a junior and six games as a senior. Despite only playing in six games, he still managed to lead the team in sacks this past season with 7.5. His production was impressive on a limited basis, but he'll need to prove to teams that he can stay healthy.

As Rapoport notes, Gustin is currently viewed as a late-round prospect. NFL.com's Lance Zierlein isn't too high on him, writing “Gustin's lack of juice or complexity as rusher could limit his upside. However, his size and ability to dig in and fight against the run could help his chances of becoming a backup who might have to keep fighting for his spot.”