Alan Pardew will speak to Jake Livermore to find out what prompted his altercation with West Ham fans on Tuesday night.
West Brom midfielder Livermore, who had been substituted during the second half, had to be escorted down the tunnel following the incident.
Baggies boss Alan Pardew admitted he saw Livermore, 28, in among the crowd at the London Stadium but did not know what had provoked his actions.
Pardew said: "The only thing I know is I see Jake in the crowd, which disturbed me. Obviously you don't want to see a player in the crowd.
"There's no way he's going in the crowd - because I know him, he's a great lad - unless he was provoked severely. That's all I know.
"I haven't had a chance to talk to Jake. I'll speak to Jake and we'll go from there."
West Ham also confirmed they would be investigating.
Hammers manager David Moyes said: "I genuinely didn't see anything. I didn't know about it, but I've been told something happened."
The incident marred a dramatic 2-1 victory for West Ham against their relegation rivals.
James McClean had fired West Brom into the lead before half-time but two goals from Andy Carroll - his first since April - lifted the Hammers out of the bottom three.
The first was a trademark header from Aaron Cresswell's cross and the second a far-post finish from a tight angle in the fourth minute of stoppage time.
Moyes added: "They were two great goals. It was a great centre-forward's header, as good as it gets. I was a centre-half and I don't think you can stop that.
"And from a tight angle, the second was a great finish.
"Some games will suit Andy more than others and I thought this one suited him. The boys are giving it a real good go to get results."