I agree with the fact that it might be difficult to determine the source of the cyst, hence most surgeons would evaluate it to make sure it is not part of any blood vessel or any lifethreatening structure. In doing an excision the anatomy might be defined intraoperatively or by histopathology (lab)
The result and diagnosis would determine if there is a need for further treatment and /or further investigations.
the only cysts that are common in that area are hydranitis suppuritiva which are pus-filled (hence do not fit) or sebacious abcess (also yellow fluid).
A ganglion cyst of one of the muscle tendons may be the best fit