Elise Amendola/Associated Press

There's a reason the source of Julian Edelman's failed drug test has not leaked yet: No one seems to know what it was.

Albert Breer of Sports Illustrated reported Edelman's positive test was "triggered by a substance that wasn’t immediately recognizable, and there are scientists analyzing it."

Edelman, 32, is appealing the four-game ban for his violation of the NFL's policy on performance-enhancing drugs.

"I am very sorry—I don’t know what happened," Edelman said in an Instagram post. "I've taken many, many tests obviously over the course of my career, and nothing like this has ever happened. I apologize to the Kraft family, my coaches, teammates and fans. As this matter is being appealed, I can't say anymore but no matter what, I will be ready to play and pursue another championship with our team and for Patriots fans around the world."

Edelman missed the 2017 season due to a torn ACL. He had recorded at least 90 receptions in three of the four previous years, becoming Tom Brady's favorite underneath target.

The Patriots got used to playing without Edelman last season but were banking on his return. They traded Brandin Cooks and allowed Danny Amendola to leave via free agency. Rob Gronkowski is the only player remaining from the 2017 roster who had 500 yards receiving.

Unlike last year, when Amendola could play the Edelman role, there is no obvious replacement on the roster. It's possible New England could take a nosedive offensively for the first four weeks if Edelman's suspension is upheld.