The east London club published a statement on social media at 16:30 GMT stating: West Ham United can confirm striker Michail Antonio has today been involved in a road traffic accident. The thoughts and prayers of everyone at the Club are with Michail, his family and friends at this time."
West Ham also said that they would provide updates in due course and did so just over an hour later, confirming that the striker was in hospital but was conscious and in stable condition.
"West Ham United can confirm that Michail Antonio is in a stable condition following a road traffic accident this afternoon in the Essex area," said the club.
"Michail is conscious and communicating and is currently under close supervision at a central London hospital.
"At this difficult time, we kindly ask everyone to respect the privacy of Michail and his family.
"The Club will make no further comment this evening, but will issue a further update in due course."
Antonio joined West Ham from Nottingham Forest in 2015 and has made a total of 322 appearances for the Hammers.
The English-born Jamaica international has scored 83 goals for the East London club in all competitions.
Antonio began his career with Tooting & Mitcham United, breaking into their senior squad in the 2008/09 season.
He quickly signed for Reading, where he would spend three years before joining Sheffield Wednesday in 2012 after a successive loan spell.