The east London club published a statement on social media at 16:30 GMT.
“West Ham United can confirm striker Michail Antonio has today been involved in a road traffic accident,” it said.
“The thoughts and prayers of everyone at the Club are with Michail, his family and friends at this time.”
West Ham also stated that they would provide updates 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.
