The player in question is not yet known.
SportsIllustrated.com reported Tuesday that the total amount of the fine is $500,000. By comparison, that is double what the NFL's New England Patriots were fined last September for videotaping New York Jets defensive signals as part of "Spygate," though Patriots coach Bill Belichick was separately fined $500,000 for his role.
That amount is also what the Cubs awarded as a signing bonus to Matt Cerda, their fourth-round selection (131st overall) from Oceanside (Calif.) High School last June. The $500,000, which Cerda confirmed that he signed for, is well above MLB's slot signing recommendations, though teams cannot be penalized for exceeding them.
Cerda said Tuesday that he was not the player that took the field before his signing was approved by the commissioner's office.
A Cubs official said Tuesday that the club had no comment on the issue, which ESPN.com first reported earlier this week.