The club is extending its community shares scheme offer to the end of February.
FC United, set up in 2005 by angry Manchester United FC fans following the take over of the Premier League club by the Glazer family, said the scheme has generated £700,000 of investment so far with another £200,000 pledged.
The scheme aims to raise £1.5m towards the FC United's own ground in Newton Heath which was given planning approval by Manchester City Council last Thursday.
Following this, FC United hopes that by extending the offer, a further wave of investors will come forward and push the total towards the target.
Adam Brown, FC United board member, said: "We're the first football club to try this approach and we're breaking new ground on what is possible for a supporter-owned club to achieve.
"Given this is the first time a football club has tried this approach, we are delighted with the reaction from our fan-base and the business community, ethical investors and anyone who wants to be part of pioneering a new way for football finance.
"The cup run has been a great boost to the club but has also stretched our resources to the limit. And we only received assurance about tax breaks on the scheme last month, so we want to give people more time to respond to this huge benefit."
In November, HM Revenue & Customs gave advance assurance that those who buy £500 of shares can claim 20% back against tax under the Enterprise Investment Scheme.
Investors can purchase £1 shares to a value ranging from £200 up to £20,000.
FC United drew 1-1 against Brighton & Hove Albion in the second round of the FA Cup to secure a place in the hat for third round.
The replay match is scheduled at Gigg Lane in Bury, where the club currently plays its home games, next Wednesday 8 December.
FC United aims to create a permanent home close to United's birthplace at Newton Heath, Manchester. The 5,000 capacity stadium will cost £3.5m to build. The funding package includes £1.5m from community shares, £500,000 from donations, with over £300,000 raised to date, and the remainder from grants.
Brown added: "There is an amazing buzz around the club at the moment and investing in shares offers individuals a way to be part of it. The tax relief alone offers a significant financial benefit, equivalent to a return of 6.5% for the first three years, and after that we aim to pay interest on the shares in the future."
FC United said community shares cannot be traded or transferred like normal shares, but shareholders who want to withdraw their investment can apply to have their funds returned from the fourth year onwards. Subject to board agreement, the club will allow not more than 10% of the total share capital to be withdrawn in any one year.
The offer is open to individuals aged 16 years old and over and businesses. All shareholders must be members of FC United but non-members can join at the time of application.
The offer will now close at 5pm on Monday 28 February 2011.