AC Milan's Kevin-Prince Boateng walked-off the pitch in protest after being subjected to racist chants during a friendly match.
Manchester United's Rio Ferdinand stoked further controversy when he defied his manager to boycott wearing an anti racism t-shirt.
The FA must do more to tackle racism and other discrimination, MPs have said.
A Metropolitan Police spokesman said the arrests were made over alleged public order offences.
– Metropolitan Police spokesman
Six males were arrested during the game at Millwall in relation to a banner being unfurled at the game. They remain in custody at this time."
Six people have been arrested over a banner, which reportedly attacked a footballer who was racially abused by a Millwall fan, police said.
The banner was unfurled in a Millwall section of the Lion's New Den ground during their 2-1 win against Derby County.
Bolton striker Marvin Sordell, was abused by fans while warming up for his side's game at the East London club's stadium on 6 October.
A 13-year-old boy was banned from the ground.
Britons think that racism is widespread in national football, and a majority feel it will be impossible to eradicate it completely, according to a poll.
After incidents involving Chelsea's John Terry, Liverpool's Luis Suarez and now alleged comments by referee Mark Clattenburg, the survey revealed four out of ten respondents agreed that racism is widespread in English football, an increase on 31 percent from June 2012.
57 percent said it would be impossible to eliminate racism from football but nearly two thirds (62 percent) said harsher penalties for racist behaviour would reduce the number of racist incidents, according to the ComRes poll for the Sunday Mirror.
After Mark Clattenburg was accused of using "inappropriate language" by Chelsea during last week's match against Manchester United, 62 percent of respondents said referees' conversations with players should be recorded.
– Rio and Anton Ferdinand
On the issue of Kick it Out, we would like to go on record to say what fantastic work they have done in the past regarding education and awareness.
However, times change and organisations need to change with them. We are more than happy to join the discussion, privately, to make Kick it Out more relevant in its fight to stamp out racism in football.
Although we have been left disappointed by the PFA and the FA's actions over the last year, as a family, we are committed to working with football's existing organisations towards the betterment of the game and to achieve immediate action.
In a wide-ranging statement released by the Ferdinand's management team, NEW ERA GLOBAL SPORTS, the pair have expressed their desire to "work with football's existing organisations towards the betterment of the game and to achieve immediate action".
In addition, they have claimed the Kick it Out organisation, whilst doing good work in the past, needs to change and have offered to work with it to make it "more relevant in its fight to stamp out racism in football".
The statement said: "It has been a year since the incident at Loftus Road. During that time, some of the deep divisions that exist in football have been exposed.
"In the coming months there will be ongoing discussions, we are sure, on finding a way forward.
"We intend to participate in these discussions, along with numerous other current and ex professionals of all races, from the grass roots upwards, across the football community as a whole."
Players' chief Gordon Taylor has announced a six-point action plan to deal with racism in football after criticism from some members.
The PFA chief executive says the union wants tougher penalties for racist abuse including making it potentially a sackable offence, culprits ordered to attend awareness programmes and a form of the NFL's 'Rooney rule' to boost the number of black coaches and managers.
The Manchester United defender Rio Ferdinand appears to have rubbished newspaper reports that he was planning to launch a breakaway union to protect the interests of black footballers).
Don't believe all u read.
Manchester United manager Sir Alex Ferguson says the issue with Rio Ferdinand was a 'communication problem' and he'll be rested for tomorrow's Champions League match against Braga.
But the Scot told a press conference that his dispute with the defender had been resolved and that his advice is that "a union is always stronger than an individual."
Rio Ferdinand was training this morning as normal ahead of Manchester United's Champions League encounter with Braga at Old Trafford tomorrow.
The defender defied Sir Alex Ferguson on Saturday by refusing to wear a T-shirt supporting the anti-racism Kick It Out campaign ahead of United's 4-2 win over Stoke, leading his manager to state publicly that the 33-year-old would be "dealt with".
But there have been suggestions that the pair resolved their differences at a meeting yesterday morning and Ferdinand did train with the remainder of his team-mates at Carrington ahead of tomorrow night's game.
The Professional Footballers Association (PFA) chairman said players are entitled to take a stance over racism.
As one of the bodies which funds Kick It Out, the PFA also defended Rio Ferdinand in the face of possible sanctions from United boss Sir Alex Ferguson.
Ferguson said Ferdinand's decision not to wear the t-shirt was "embarrassing" and promised to "deal with it".
PFA chairman Clarke Carlisle told BBC Radio 5 Live: "We will definitely monitor the [United] situation very closely and make sure Rio Ferdinand's rights as a human being, never mind as a footballer, are not undermined in this position.
"Everyone has a right to free speech - just like you can't coerce anyone into shaking hands, you can't make somebody wear a T-shirt - although I do personally believe that joining in with the campaign is the best way forward.
"And then for all these players to get together and put what it is they want down on paper so we together as a union - all the players, one with another - can make those changes and move forward."