The letters were reportedly found by a colleague who was performing a routine operation on the unnamed patient.
University Hospitals Birmingham NHS Foundation Trust confirmed that they were investigating the claims made against a surgeon at the Queen Elizabeth Hospital in Birmingham.
The surgeon has been suspended while an internal investigation is carried out, the Independent reported.
The news comes after concerns were raised by a report published by NHS England in mid-December which exposed mistakes made by its staff.
Errors which should never happen, or “never-events”, included patients being given the wrong blood type, and the wrong patient undergoing surgery.
148 “never-events” occurred between April and September 2013, with 69 of those involving objects, such surgical swabs, being left inside patients after surgery. 37 patients had surgery performed on the wrong part of their body, while the wrong implant or prosthesis was administered to 21 patients.