Stoyanov faces ban after failing drugs test
Bulgaria international Stoyanov, 25, tested positive for the banned stimulant Methylhexanamine after CSKA's 1-0 league win over city rivals Levski on October 28.
CSKA, 31-times Bulgarian champions, said the analysis of Stoyanov's B sample confirmed the presence of the banned substance in his urine.
"We have nothing to hide, it's a fact," CSKA's lawyer Radostin Vasilev told local media, adding that the club would give more details at a news conference.
Stoyanov, who was instrumental in helping CSKA to win the Bulgarian Cup last season, will find out the length of his ban in the next three weeks.
"The possible sanction is between six months and two years," said Belcho Goranov, general secretary of the Bulgarian Olympic Committee (BOC) which will decide the length of Stoyanov's suspension.