The 24-year-old was delisted by the Saints at the end of the 2013 season after he tested positive for a banned stimulant contained in an energy drink.
The suspension has been back-dated to August 20 this year, meaning the Egyptian-born goal-sneak will have to sit out the entire 2014 season and will not be able to return to football until February 2015.
Any hopes Saad had of being selected by the Saints in Wednesday's rookie draft are likely to have been brought to an end by the tribunal's decision, but the club could still try to take him in one of the 2014 drafts.
In a statement released on Tuesday night, the club said they would continue to support Saad through his time away from the game.
"The St Kilda Football Club can confirm that Ahmed Saad has today received an 18 month suspension from the AFL Tribunal after he inadvertently took a substance on the AFL Anti-Doping prohibited list," the statement said.
"Following acceptance of a provisional suspension that commenced on 20 August this year, Ahmed’s period of ineligibility will expire of 20 February 2015.
"The Club will continue to provide the appropriate welfare support and assistance to Ahmed."
Saad played 29 games for the Saints and kicked 45 goals after making his debut in round 6 of the 2012 season.