Insall, who is currently on loan at East Fife, tested positive after a match against Livingston on March 11.
The UK Anti-Doping (UKAD) has reportedly informed the League One outfit, who passed on the news to his parent club.
Insall joined Hibs in summer 2015 and is contracted with the club until 2018.
Should UKAD uphold the findings, Insall could face a lengthy ban.
According to a Sunday newspaper report, the player is contesting the result - claiming he had taken cold medication earlier that day.
Insall, who has not made a competitive first-team appearance at Hibs, has scored 14 times in 50 games for East Fife.
Hibs have declined to comment.