The Premier League club were deemed to have made an unauthorised approach to Jamaal Lascelles, who was then under a scholarship agreement at Nottingham Forest, in 2010.
Andy Niedzwiecki, the agent who represented Lascelles at the time, has been fined £10,000.
Lascelles himself has been "severely warned as to his future conduct".
A statement on the FA's website confirmed the sanctions and added: "The time-frame for any appeal has passed."
Lascelles, now 20, is still at Forest but has been linked with a number of leading top-flight clubs.
Get the best features, fun and footballing frolics straight to your inbox every week.
Thank you for signing up to Four Four Two. You will receive a verification email shortly.
There was a problem. Please refresh the page and try again.