St Kilda have named forward Ahmed Saad as an emergency for Saturday night's away AFL match against Brisbane.
The league is investigating whether the 23-year-old Saint has breached the league's anti-doping code after providing an irregular sample in July.
The AFL announced late on Friday afternoon that the Saints had brought in Saad in place of Trent Dennis-Lane as one of their three emergencies for the match.
Before leaving for Brisbane earlier in the day, coach Scott Watters said he believes Saad's positive test was an isolated incident with no further implication for the club.
If charged, Saad would face an AFL Tribunal hearing and, under the anti-doping code, use or possession of a prohibited substance can lead to a two-year ban for a first violation.
The Saints released a statement on Wednesday, confirming Saad had tested positive to a substance which they said was permitted for use out of competition but not in competition.
The Saints said Saad was surprised and extremely disappointed.
Watters refused to give any further detail at Friday's media conference about how Saad came to take the substance, his current mental state or even how the news had affected other Saints players.
He also initially refused to comment on whether it was an isolated incident, before it was put to him that refusing to answer that question might lead to speculation it was a broader problem.
"I think it would be very misleading for you to lead this conversation down that path," Watters told reporters at Melbourne Airport.
"This is an isolated incident that's being treated by ASADA."
Saad hasn't played in the Saints' AFL side since the round 15 game against Fremantle, although he has played VFL football since.
He is allowed to keep playing under the anti-doping code as he is yet to be issued with an infraction notice.
The Saints have named stars Nick Riewoldt and Lenny Hayes for Saturday night's Gabba clash with Brisbane, despite both being in serious doubt after they ended last weekend's clash with Geelong sitting on the bench injured.
"It's great news for us," Watters said.
"Obviously there were a lot of concerns about both of them."
Riewoldt injured his foot and Watters said while it was initially very concerning, scans found it was a chipped bone spur, which the coach labelled a minor injury which could be cleaned up in the post-season.
He said Hayes was initially diagnosed with a hamstring strain but scans gave him the all-clear.
But defender James Gwilt has been forced out by a knee injury, further depleting the Saints' undermanned backline.
