Nottingham Forest midfielder Nathaniel Chalobah claims he was subjected to racist abuse by a section of Millwall's home support during Tuesday night's Championship meeting in south London.
The 18-year-old, who is on loan from Chelsea, originally told Forest assistant manager David Kelly that he had allegedly been abused while receiving treatment for an injury in the opening minutes of the 2-2 draw.
In a statement published on Forest's official website on Wednesday night, Chalobah was said to be "upset by the alleged abuse and struggled to keep his concentration during the interval as a result."
The statement continued: "Nottingham Forest treat any incident of this nature extremely seriously and will be liaising closely with the relevant authorities in their investigation of this issue.
"Both clubs are in communication regarding the alleged incident and hope to uncover the truth as quickly as possible for all concerned parties."
England under-21 international Chalobah, who is on loan at Forest until January, scored the final goal of four at the New Den to salvage a point for Billy Davies' side.
He has scored two goals in seven appearances since moving to Nottingham in September.
A Football Association spokesman confirmed it would be investigating the matter fully by speaking to both clubs, anti-racism campaigners Kick It Out and the police.
A spokesman for the Metropolitan Police later confirmed the force had been made aware of the claim and would work with both clubs to investigate the matter fully.
Millwall were unavailable for comment.