Professional Footballers Association chairman Clarke Carlisle has criticised Rio and Anton Ferdinand for choosing not to support last year's anti-racism T-shirt demonstration.
The brothers, Manchester United defender Rio and then-QPR player Anton, were among several prominent black players who opted not to wear shirts before a round of Premier League fixtures last October.
Carlisle wrote in his new autobiography 'You Don't Know Me, But... A Footballer's Life'.
In extracts published in the Daily Mail, he added: "Kick It Out is one of few bodies doing something positive about the issue, but there are some who evidently feel it is not doing enough.
"Rio and Anton Ferdinand were among a group of high-profile abstainers along with Joleon Lescott, who has not worn one since Newcastle's Turkish midfielder Emre was cleared of racially abusing his Everton team-mate Joseph Yobo, and Jason Roberts.
"At least Jason was vocal about his reasons. I don't mind people disagreeing but at least say why."