Wayne Rooney says football must not tolerate the "disgraceful and mindless behaviour" of fans booing anti-racism gestures.
Supporters were back at Millwall on Saturday for the first time since 29 February, 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.
Further comments from yesterday's game.... pic.twitter.com/7T25MmMDwI— Wayne Rooney (@WayneRooney) December 6, 2020
"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.
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.