Ferdinand, whose brother Anton was racially abused by Chelsea captain John Terry last year, did not wear a Kick It Out campaign t-shirt in the pre-match warm-up before United's 4-2 win over Stoke on Saturday, despite boss Alex Ferguson saying on Friday that all his players would support the equality group.
Ferguson has hinted he will punish Ferdinand for his actions, describing the incident as "embarrassing" and promising to "deal with it".
However, several other players around the country on Saturday also snubbed the T-shirt in protest at Kick It Out's failure to demand harsher punishment for racist incidents.
Reading's Jason Roberts, Stoke's Kenwyne Jones and Manchester City's Joleon Lescott all took part in the protest and PFA chairman Clarke Carlisle promised to keep track of the situation to ensure Ferdinand doesn't suffer for sticking up for his principles.
"We will definitely monitor the 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," Carlisle told BBC Radio Five Live.
"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."
Former Burnley defender Carlisle urged Ferguson to follow the examples of Reading boss Brian McDermott and Newcastle manager Alan Pardew in allowing Ferdinand to explain the reasons behind his decision.
"There are two sides to this one. First of all, Sir Alex Ferguson is continual in his unwavering support for the Kick It Out campaign which is commendable and what we all want to see but you can't vilify or coerce any individual for making a stand," Carlisle said.
"Ferguson said he was embarrassed and that is because of the statement he had made but Brian McDermott and Alan Pardew, these guys said they had entered into dialogue with their players and listened to the reasons for them making their stand.
"So I would sincerely hope that Ferguson now speaks with Rio Ferdinand and asks him why he wanted to make that stand and hopefully supports the position he is in and it isn't seen as a player-against-manager situation."
Source: AFP
Source: AFP