Getty Images

Patriots wide receiver Julian Edelman has acknowledged he is facing a four-game suspension under the NFL’s policy on performance-enhancing substances, but he also said he doesn’t know what happened. It appears the league’s drug testing experts aren’t completely sure what happened either.

According to Albert Breer of SI.com, Edelman’s result was triggered by a substance that wasn’t immediately recognizable, and the drug testers are still analyzing it.

That might sound strange, but it’s not unprecedented for the drug testers to need time to determine what substance a player took: In 2003, four Raiders players tested positive for tetrahydrogestrinone, or THG, a substance that wasn’t initially detectable in urine tests. It was only after the lengthy Balco investigation that drug testers re-tested stored urine samples and detected the substance.

Breer adds that Edelman’s test took place a couple months ago, during the offseason. That means that whatever substance he tested positive for, it wasn’t a stimulant like Adderall. Use of stimulants in the regular season is considered a performance-enhancing substance issue, but during the offseason it’s considered a substance abuse issue.