Derby County caretaker manager Wayne Rooney has urged football fans to not “tolerate or accept” the actions of “mindless” fans who take part in discriminatory behaviour.
Some Millwall fans booed the players taking a knee before Saturday’s game against Rooney’s Derby at The Den.
“It is really important that the vast majority of us show respect and support of each other,” said Rooney, 35.
Millwall say they are “dismayed and saddened” by the booing.
Millwall said staff and volunteers have worked hard to enhance the south London club’s reputation but admits there is still “much work to be done”. The Lions added they are committed to doing it to “be a force for good”.
The Den was able to host 2,000 home fans for the first time this season after the second national lockdown was lifted.
The return of spectators was overshadowed by the pre-match incident.
The Football Association and anti-discrimination body Kick It Out have condemned the booing.
Former England captain Rooney, whose side won Saturday’s game 1-0, said afterwards it was “disappointing and upsetting” to hear the booing from supporters.
On Sunday, he released a longer statement about the incident and said Derby had been warned before the match about the potential response of some home fans.
“We were made aware of the possibility of a planned disruptive response during the taking of the knee in support of the Black Lives Matter campaign,” said the former Everton and Manchester United player.
“On behalf of Derby County Football Club, I want it to be clear to everyone associated with the club that we represent all sectors of our community regardless of colour, gender or sexuality.
“It is important we do not tolerate or accept the actions of the mindless few.”
Derby forward Colin Kazim-Richards described the incident as “an absolute disgrace”.
Players, officials and staff at Premier League and English Football League games have been taking a knee pre-match since football restarted in June in order to show their support for the Black Lives Matter movement for racial equality.