Defender Casserly, 23, was on the Tigers' list from 2006-08 and has spent the past two seasons playing with WAFL club Swan Districts.
He is one of three players training with Richmond who are battling for the club's final rookie spot.
Casserly is reported in News Limited publications to have tested positive to a drug similar to pseudoephedrine, which contains stimulant properties, after feeling unwell before the grand final and taking a cold and flu tablet.
Swan Districts football operations general manager Phil Smart said Casserly would protest his innocence at a hearing expected in the next two weeks.
"We will be defending it vigorously," he said.
Casserly was set to play for Richmond in Friday night's match against the Indigenous All-Stars in Alice Springs, but the clash was cancelled due to the threat of severe weather.
