New laws could be put in place to drive sweeping changes to the way English football is run, following failures by the sport's authorities to change the governance of the game.
A committee of MPs said the Premier League wielded too great an influence over the game in England and ordered reforms.
But the culture, media and sport select committee's said it had been "very disappointed" by the football authorities' response to its proposals for reform made in July 2011.
Its concerns cover financial management, the balance of power between the Premier League and the Football Association, and major financial risk-taking.
The committee proposed shaking up how the FA operates and making clubs adhere to financial rules, regulated by a licensing system.
But in a follow-up report MPS said the response of the football authorities to the proposals had been "very disappointing".
Committee chairman John Whittingdale said: "While some progress has been achieved, much greater reform in football is needed to make the game inclusive, sustainable and driven from the grass roots, where it should be.
"The proposals for reform so far simply don't address the fundamental problems: the licensing model, the way supporters are engaged at club level and the membership of the main [FA] board, which is not fully representative or able to balance interests adequately.
"In addition, the financial proposals were hugely disappointing: the financial risk-taking by clubs is a threat to the sustainability of football as a family and community-orientated game, which it should be.
"If football cannot reform itself, the Government should introduce legislation as soon as practically possible."
Recommendations by the committee include:
- Reducing the size of the FA board, and make FA executives and non-executive directors be in the minority compared to the "vested interests" of members appointed by the professional and amateur game;
- The Premier League and Football League should be limited to one FA board member each - the leagues currently have two apiece;
- The FA board should have fans' representation.
- Full information on the ownership of clubs should be made publicly available;
- The FA should regulate a financial licensing system, and not leave it to the Premier League and Football League;
- If spending controls such as financial fair play are not adopted by the clubs, legislation should be brought in to impose financial discipline;
- Long-term funding plans should be agreed for Supporters Direct (SD), a group that promotes the value of supporter ownership and influence.
Sports minister Hugh Robertson insisted the warning on legislation was no empty threat. He said: "If football does not deliver the reforms then we will look at bringing forward legislation."
In a joint statement, the FA, Premier League and Football League insisted the necessary reforms would be implemented.
It said: "Significant headway has already been made on many of these proposed reforms, not least on sustainability and transparency. The remaining reform proposals are the subject of consultation within the game and we are confident that the necessary progress will be made."
In welcoming the report, SD chief executive David Lampitt said: "The committee has clearly been spurred on by what they called the 'lack of direction and urgency' of the football authorities and has recognised that a few minor changes do not add up to meaningful reform.
"A timetable for proper change is now required, backed up by government intervention if it is not delivered upon.
"It is supporters who sustain the game economically - whether through tickets or TV subscriptions - and who have the long terms interests of the game at heart."