West Ham will launch an investigation into how two separate pitch invasions were allowed to happen in Wednesday's Carabao Cup defeat to Tottenham.
The Hammers will work with London Stadium landlords LLDC to discover how the two culprits evaded security, while the FA will also look into the incidents and could charge West Ham.
The Daily Mail reports that the first pitch invader ran on as Tottenham were preparing to take a corner in the 75th minute. After the man had been accosted by police, Spurs took the corner and Fernando Llorente scored their first goal.
The second pitch invader ran onto the field in the 90th minute wearing a Halloween mask. Both supporters will receive lifetime bans from the London Stadium.
Speaking after the match, West Ham manager Manuel Pellegrini said: "Those things aren’t for football. One of the most important things of the Premier League is how it is organised. It is not good for football."
The Sun reports that there were also violent clashes in the stands when two Tottenham fans were ejected for sitting in the home end. Some West Ham fans threw drinks and then punches as they were escorted out of the stadium.
Some people who were at the game have also reported that racial abuse was directed towards Tottenham's South Korean striker Son Heung-min, who scored two goals to send his team through to the quarter finals.
This is not the first time West Ham have failed to control their supporters this year, with four separate pitch invasions occurring during their Premier League defeat to Burnley in March.