FIFPRO Europe president David Terrier said FIFA was trapped in a "real war" with a breakdown of trust among federations and confederations following president Gianni Infantino's botched proposal to sell off commercial rights to the World Cup.
Infantino, who is seeking reelection in March, has faced open revolt in the last two weeks after three confederations - UEFA, AFC and CONCACAF - attacked his conduct and called for him to quit.
"At this point, the question is no longer whether Gianni Infantino should stay on or resign. It's clear that a real war has broken out, with a loss of trust from many federations and confederations," Terrier told Reuters.
"I'm not saying Infantino absolutely has to go. I think that, given the current context, the question almost doesn't even arise anymore.
"The issue is not whether he should resign or not. What we need are reforms, and they are indispensable. There is a real lack of trust and serious doubts about how the system operates."
Following a crisis meeting in Morocco last week, FIFA apologised to its 211 member associations for mistakes in the handling of the proposal and said its leadership had reaffirmed its full support for Infantino.
'Unacceptable style'
FIFA also warned against efforts to undermine Infantino, saying attempts to challenge his leadership must follow the governing body's statutes and democratic procedures.
But Terrier warned FIFA risked repeating the mistakes that had plagued the organisation before the corruption scandal that brought down former president Sepp Blatter in 2015.
"This style of governance is no longer possible or acceptable; it's exactly what we have been denouncing for years. We are in a worse situation now than when Blatter resigned," he said.
"If we continue with the same system, we will face the same suspicions and football will not be placed in a positive situation. We've reached a point where there is too much suspicion, and reforms are necessary.
"The FIFA president should be the one to drive and support them. In such a case, he must be willing to put his mandate on the line. Without that, whatever happens will be a defeat for football."
'Last opportunity'
FIFA insisted that all actions taken over the proposal complied with its regulations and stressed that mistakes related to process and communication rather than breaches of governance rules.
However, Terrier said the crisis has shown it may be "the last opportunity to change the system".
"These powers must be shared, with a president who is a guarantor, but who does not hold all the power," he said.
"It is the last chance we have to secure reforms and put mechanisms in place to protect football.
"FIFA's administration is not in a position, not able, to act as a counter-power or as guardian of the laws, statutes and regulations that apply - including to its own president."