Sunderland have avoided a points deduction after it was revealed Ji Dong-won played in four top-flight matches when he was ineligible.
The Daily Mail says club secretary Liz Coley departed abruptly after the administrative error left Sunderland facing a Premier League investigation for breaching rules B14.5 and U11.
The League have fined the club substantially but not deducted points despite an FA statute saying they should have been docked or made to replay their game against Southampton in August, when Ji helped them win a point.
Sunderland were also fined by the Football League after striker Ji played in a 4-2 victory over MK Dons in the Capital One Cup when he wasn't eligible to play.
MK Dons are understood to be furious that Sunderland were not thrown out of the competition once the error was spotted.
They went on to lose in the final against Manchester City.
The 22-year-old South Korea striker, who joined Sunderland in 2011, was sent out on loan to German club Augsburg last season.
When he returned, Sunderland had to wait for international clearance before he could play for them but they never got it.
