The Football Association has written to Manchester City to ask the club for its response to a tweet sent by midfielder Bernardo Silva, reports BBC Sport.
Silva compared City team-mate Benjamin Mendy to the character on the packet of Conguitos - a sweet brand available in Spain and Portugal.
The anti-discrimination charity Kick It Out had earlier called on the FA to act after the governing body confirmed it was investigating.
Manchester City declined to comment.
"We are extremely disappointed to see the tweet posted by Bernardo Silva," said the anti-discrimination body.
The post was published at 12:44 BST on Sunday but was deleted at 13:30.
Bernardo then tweeted: "Can't even joke with a friend these days."
France defender Mendy and Silva are close friends and played together at Monaco before both joined City in 2017.