Warner quit FIFA in disgrace following a corruption scandal in 2011, after three decades as an executive committee member.
The Trinidadian politician has continued to be caught in allegations surrounding payments made by another ex-FIFA member, Qatar's Mohamed Bin Hammam.
Blatter is expected to announce on Wednesday at FIFA's Congress in Sao Paulo that he will stand for a fifth term as president. But Warner, who played a key role in securing Blatter's original election, said it was time he stepped down.
Warner said: "If Blatter had one modicum of decency he wouldn't even be at FIFA still.
"I have been with FIFA for 30 years....I am still the longest serving elected officer of FIFA, and under Mr Blatter? I am saying to you under Mr Blatter, FIFA will never change."
Meanwhile, on Monday Blatter claimed allegations of corruption surrounding the Qatar 2022 World Cup bid have been steered by "discrimination and racism".
The Sunday Times published further allegations this week regarding Bin Hammam, claiming it has received ''hundreds of millions'' of documents some of which show payments he authorised to football officials during the bidding process for the tournament.
However, Blatter told the Confederation of African Football (CAF) Congress in Sao Paulo on Monday that the media reports are a "storm against FIFA".
The Swiss added: "Sadly there's a great deal of discrimination and racism and this hurts me. It really makes me sad."
African officials were among those alleged to have taken payments from Bin Hammam, according to the Sunday Times.
CAF responded by issuing a resolution on its website Monday condemning the claims as "deliberately hateful, defamatory and degrading".
Bin Hammam was banned from football for life by FIFA in December 2012 over ''conflicts of interest'' while president of the Asian Football Confederation (AFC).
FIFA's chief investigator, Michael Garcia, has this week completed his assessment of the bidding process for the 2018 and 2022 World Cups, due to be finished this week - although the findings will not be made public until later this summer.