The Football Association has confirmed investigations are under way into crowd-related incidents at Millwall and Colchester after some supporters booed players taking a knee during their home games on Saturday.
A statement from the FA said: "The FA can confirm that investigations are underway into crowd-related incidents at both The Den and JobServe Community Stadium on Saturday 5 December 2020.
"Observations have been sought from all of the relevant parties and they will have until Thursday 10 December 2020 to provide their respective responses."
Millwall say they are "dismayed and saddened by events which marred Saturday's game against Derby County".
QPR will change their policy on taking a knee for Tuesday's game at Millwall, live on Sky Sports, in a show of "solidarity" following booing at the Den.
Players from the west London side stopped taking a knee earlier this season following director of football Les Ferdinand's comments that the action had become "diluted".
QPR boss Mark Warburton echoed Ferdinand's calls for "positive action", rather than "gestures", but says his squad will once again take a knee after discussing their response to the scenes that overshadowed Millwall's game against Derby on Saturday.
Colchester owner: Booing fans are not welcome
Colchester owner Robbie Cowling says fans who want to boo players taking a knee are not welcome at the club.
The U's beat Grimsby 2-1 in Saturday's Sky Bet League Two clash, but that victory was overshadowed by a number of fans booing the players' anti-racism gesture before kick-off.
"The game is being talked about because of the ridiculous actions of a few who decided to boo our players whilst they took the knee before kick-off," said Cowling, in a statement.
"It is undeniable that black and other ethnic minority people are still the victims of racism, and the black footballers and staff at Colchester United feel that they are in a position of privilege that has been fought for through the blood and sweat of their ancestors. A position that in 2020 the average black person is still not afforded.
"Those taking the knee, and supporting the taking of the knee, not only show their willingness to support the drive to eradicate racial oppression but force it to be a talking point even when it's uncomfortable.
"Maybe those that booed on Saturday might now understand what this gesture means to our club and will at the very least remain silent during future games whilst the players continue to take the knee before each kick-off.
"Alternatively, they should just stay away from our club because anyone that still wants to boo now that I have explained the purpose and importance of the taking of the knee is not welcome at our club.
"I will be happy to refund anyone for the remaining value of their season permit if that is the reason they feel they can no longer attend our games."
PFA: Racism is a human, not political issue
The Professional Footballers' Association (PFA) has reiterated its support for players taking a knee and insists the act is a "human rights issue", rather than political.
The players' union also strongly condemned the section of Millwall supporters who booed and urged the club to identify those responsible.
"This is a human issue, I can't stress that enough, it's about the players. Booing isn't illegal and that point has been made, but it can be inappropriate," PFA equalities officer Iffy Onuora told Sky Sports News.
"If there was a live band on stage and you booed them, how long would they stay on? How long would a theatre group stay on stage for if they were booed?
"These are people going to work and exercising their right to protest."
In a statement, the PFA also said: "The decision to take the knee - as a result of the death of George Floyd in the USA and the global tide of support for the BLM movement - was a player-led decision in solidarity and support for Black people facing racism. We have all seen players face racist abuse on and off the pitch - this is not a political issue it is a human rights issue.
"The PFA fully supports the players' right to take the knee, whilst understanding it is the responsibility of the football authorities to continue to push and challenge inequalities in football.
"The closed stadiums have been a respite for players receiving on-field abuse, although it has not stopped continued abuse online.
"The perpetrators at Millwall should be easily traced given stadium restrictions and we call on the club to act swiftly to identify the section of the crowd who booed the players.
"Whilst booing is not a crime, it is a sad indictment of the lack of understanding and empathy for the players' fight against racism and discrimination."
Agbonlahor: I'd ask for a move away from Millwall
When asked what he would have done in the position of Millwall's black players, former Aston Villa striker Gabby Agbonlahor said he would definitely consider his future at the club.
"You want to keep playing because it's not the whole of the Millwall fanbase, it's a certain group of them that are doing it," he told Sky Sports News.
"I feel as though I would probably have played on but I'd be thinking to myself, after the game, that's me done. I'm going to see out December and in January I'm going to ask my agent for a move.
"I wouldn't want to play for that club if some of your fans are going to do that and insult and disrespect something that means a lot to you as a player. Why would you want to go out and try your hardest for that club?"