The 64-year-old has revealed he was accosted by an unnamed player's representative and has called for the FA to impose a cap on the earnings that agents can make from transfers
Agents’ roles in modern football has been the subject of heavy debate in recent times, with QPR manager Harry Redknapp likening their behaviour to “gang warfare”.
And Sullivan has revealed the lengths some agents are prepared to go to to secure a deal, comparing them to “scavengers”.
"In this window, I have had an agent threaten me and threaten one of our West Ham players with physical violence, because he thought he was being cut out of a deal,” Sullivan told The Daily Mail.
"I heard of three or four agents trying to jump in on other deals. Some of these people are like scavengers.
"It was all deeply unpleasant and I'm glad it's over. Now we can get on with the football.”
Sullivan went on to agree with Redknapp’s comments and called for the Football Association to cap the astronomic amounts that are now commonplace among agents during transfer negotiations.
He continued: "Harry Redknapp was right: it feels like gang warfare out there and I can see it spilling over into violence in the future, unless there is legislation from the FA to curb the practices.
"We are talking millions of pounds here around a transfer and not enough deals to go around. There are too many agents and not enough transfers to feed them.
"Agents who would once demand €57,500 for their part in a transfer, now want €575,000 to €1.1 million to either bring a player or keep a player. It is quite outrageous and the FA should cap the amount paid to agents for their work.
“I heard of one agent, who took over representation of a player for one day, and he wanted to be paid between €1.43m and £1.72m for his part in negotiating a new contract."