Wayne Rooney says football must not tolerate the "disgraceful and mindless behaviour" of fans booing anti-racism demonstrations.
Supporters were back at Millwall on Saturday for the first time since February 29, with London placed in tier two of the current system of coronavirus restrictions, but it was the actions of some spectators which took centre stage ahead of the 3pm kick-off against the Rams.
Some of the 2,000 home crowd booed when players from both sides took a knee ahead of kick-off and, in a statement on Twitter, interim Rams manager Rooney said: "Yesterday I witnessed disgraceful and mindless behaviour by a large section of the Millwall supporters in the stadium.
"We were aware of the possibility of a disruptive response during the taking of the knee in support of (Black Lives Matter) but nothing prepared us for what we heard.
"It is really important that the vast majority of us show respect and support of each other and do not tolerate or accept the actions of the mindless few."
Colchester fans also booed when players took the knee ahead of their game against Grimsby later on Saturday.
Environment Secretary George Eustice insisted players should be free to express their views as they wish and be respected.
Eustice, when shown the Millwall clip during an interview on Sophy Ridge on Sunday, told Sky News: "There has been problems obviously with racism in football in the past. It is right that that is called out and challenged when we see it.
"It doesn't have any place in society today and if people choose to express their view in a particular way, that should always be respected.
"My personal view is that Black Lives Matter – capital B, L and M – is actually a political movement that is different to what most of us believe in, which is standing up for racial equality.
"Each individual can take their own choices about how they reflect this and I know a number of people feel quite strongly and have taken that approach."
It has been clarified to the PA news agency that Eustice meant players should be able to express their views in the fight against racism and was not suggesting fans who booed the teams taking a knee should be respected.
Nevertheless, Derby first-team coach Liam Rosenior criticised Eustice's response.
Rosenior told BBC Radio 5 Live: "What hurt even more than the booing is the response of George Eustice this morning.
"Being a cabinet minister and conflating a positive, unifying message as a message of activism, and politicising something that every single person on this planet should be supporting.
"It's not a political message, let's make this absolutely clear. This is a message about unifying our country. When top political figures are creating division, how difficult is it at ground level?"
A Millwall statement on Sunday morning read: "Millwall Football Club was dismayed and saddened by events which marred Saturday's game against Derby County.
"The club has worked tirelessly in recent months to prepare for the return of supporters and what should have been a positive and exciting occasion was completely overshadowed, much to the immense disappointment and upset of those who have contributed to those efforts.
"The club will not allow their fine work to be in vain. The players are continuing to use the biggest platform they have to support the drive for change, not just in football but in society generally."
A Colchester statement read: "Colchester United are fully behind any and all of our players and staff who take a stand against any form of discrimination.
"We also condemn the behaviours of any supporters that actively voice opposition to those activities."
Callum Harriott, who scored the Us' winner, labelled the booing "ridiculous" on Twitter.
Kick It Out chair Sanjay Bhandari admitted he was "saddened" by the behaviour of fans at Millwall.
In a statement to PA, he said: "We urge the players to continue using their platforms and their voices to support this fight.
"We applaud the players of Millwall and Derby for taking a stand and defying the hate shown by some fans today."
