Everton have launched an investigation after a missile was thrown at Ross Barkley.
Barkley received a hostile reception upon his first return to Goodison Park last weekend since securing a £15 million move to Chelsea in January 2018.
An object was aimed in the midfielder’s direction in the seventh minute of Sunday’s 2-0 win as the visitors took a corner in front of the Gwladys Street end.
Although the object did not hit anyone, the Blues have opened a joint probe with the Football Association and pledged ‘robust action’ against the perpetrator.
English football’s governing body has also written to both clubs asking for their observations on the incident.
“We are investigating the alleged incident and reviewing footage,” Everton confirmed to BBC Sport.
“If anyone is found responsible for this or other such incidents, the club will take robust action.”
Separately, the FA confirmed that Marco Silva has accepted a charge of improper conduct relating to his behaviour after Everton’s 3-2 defeat at Newcastle.
Silva received a £12,000 fine for confronting referee Lee Mason following the game at St James’ Park on March 9 over decisions he had made in the fixture.