The Football Association is investigating claims made by a Bolton player that he and three team mates were racially abused by a fan during their match against Millwall.
Marvin Sordell, 21, tweeted about the alleged derogatory remarks.
Both clubs and the Met Police are also investigating his claims.
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Officers were given the touching letter at Brixton Station while they were on a reassurance patrol after yesterday's attack
The 52-year-old had previous convictions for violence but was not on the anti-terror watchlist.
In a statement Charlton Athletic said: Keith was a true hero who will be greatly missed by all the Charlton family and everyone at the club.