Sullivan and fellow co-owner David Gold were forced to flee their seats in the directors’ box as fans crowded around them with thrown missiles mixed with chants of “sack the board” and “you killed our club”.
Brooking cut a lonely figure as he sat in the directors’ box alone for the final stages of the match that saw West Ham slip to 16th in the Premier League, just three points above the relegation zone.
And Brooking said Sunday that Sullivan had been struck.
“I think a coin did hit David Sullivan, his glasses,” Brooking told BBC 5 Live.
“I didn’t see it myself but I did have that confirmed, which was part of the reason why the people in the directors’ box had to go inside to save any more problems like that.”
West Ham said an emergency meeting had been called with all London Stadium stakeholders, which includes Gold and Sullivan, whose decision to uproot the club from Upton Park to the site that hosted London’s 2012 Olympic Games has caused resentment.
Saturday’s events are being investigated by the Football Association and the Premier League as several West Ham supporters also invaded the pitch.
West Ham captain Mark Noble grappled one fan to the floor and team-mate James Collins marched two others away, whilst Burnley players and staff allowed frightened young supporters take shelter on their bench.
Brooking believes stewards were not equipped to deal with the situation.
“The actual level of aggression was something I couldn’t believe West Ham fans would get involved with,” he added.
“A lot of the stewards who are on duty on matchdays are not West Ham people – they’re actually stadium people and sometimes until they get a job there haven’t had any experience dealing with football crowds.
“They were quite young and couldn’t deal with the aggression they were faced with.”