The 34-year-old was dismissed by the Football Association last week for committing "inappropriate and unacceptable behaviour" while in a previous role.
The results of a safeguarding investigation in 2015 were only recently brought to the attention of the FA, but it was initially ruled that Sampson "did not pose a risk" working in football.
It has now been reported by the Daily Mail that between 2009 and 2013 when the Welshman was working at Bristol Academy, he had a relationship with one of his players who was over the age of 18.
It is believed that the woman involved does not want to discuss the relationship, nor does she have any problems regarding her past with Sampson.
On Monday, the FA board held a meeting to discuss the governing body's hiring process after receiving criticism for its perceived lack of due diligence.
In a statement, the FA insisted that the "right procedures" are in place to prevent a similar situation arising and that "historic processes" will be looked into.