The secretary general of FIFA, Jerome Valcke, has in turn retained another American lawyer, Barry Berke, a FIFA spokesman told AFP.
Cullen, 67, was a federal attorney in Virginia and is currently the head of the high-powered firm of McGuireWoods LLP, which is based in the US state, and has offices in London and Brussels.
He is also a close associate of FBI director James Comey and worked for Tiger Woods's ex-wife Elin Nordegren when the golf superstar's marriage was falling apart.
New York-based Berke once represented banking giants JP Morgan Chase after the global financial crisis.