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.
More top news
The Suitsy: Man creates business suit onesie
Alex Salmond has announced his intention to end a 24-year career at the forefront of Scottish politics. Here is a brief look at his career.
Britain is among the least devolved countries in the world, figures from the RSA show.