They had previously hoped to have a deal for the Championship club, who are in administration for the third time in four years, agreed by Friday.
The Bulls said in a statement "it had not been possible to complete the due diligence in the time available" but work would continue over the weekend.
Joint administrator Gary Pettit asked fans to "remain patient".
He added: "My legal team and my colleagues will continue to work hard over the weekend to give every prospect of success for the survival and renaissance of Bradford Bulls.
"Obviously, we wish to end the uncertainty for all concerned as quickly as is possible. We recognise and understand the human aspects for everyone (and their families) who has the best interests of Bradford Bulls at heart.
"I would reiterate that it is crucial we obtain the right deal - rather than the quickest deal - for the club's future."

Thousands of pounds were allegedly stolen when security guards were targeted at the Hatfield Avenue Shell garage in Fleetwood on Wednesday.
An axe was said to have been thrown at a police car during the raid, while a woman was dragged out of her vehicle.
Four men from the Bolton area, aged 22, 24, 27 and 32, have been charged with two counts of robbery.
They were also charged with dangerous driving and threatening a person in a public place with a bladed or pointed article.
They are due before Blackpool magistrates later.

Straker, 27, has been without a club since leaving York in January, where he made 27 appearances.
He began his career at Crystal Palace and helped Aldershot Town win the Conference title in 2008, before moving to Southend United.
Grimsby are currently third in the National League, having lost only one game in the league since October.

Producers of precious metals were particularly hard hit. Analysts blamed falling prices for gold and silver and adverse currency movements.
Fresnillo, which owns the world's biggest silver mine, was down 4.5% and Randgold was down 4.2%.
"Gold is in no man's land," said Alastair McCaig, market analyst at IG Index.
He says that investors are concerned that gold could fall below $1,200 dollars an ounce, which would make some gold mines unviable.
Gold is currently trading at $1,266 dollars an ounce.
In China iron ore prices fell to the lowest level in almost five years, which hit shares in other miners.
Rio Tinto fell 0.73% and BHP Billiton was down 0.37%.
BP was 2.59% higher. Shares had slumped 6% on Thursday after a US judge found the firm "grossly negligent" over the 2010 oil spill.
The ruling has made investors cautious over the firm.
"I'm not buying BP here. The ruling opens up the door in the United States to more fines for BP," said Beaufort Securities sales trader Basil Petrides.
"The US government has got its knife out for BP and it's sharpening the blade," he said.
On the currency markets the euro was trading 0.13% higher, but still below the $1.30 level.
It fell below the $1.30 level on Thursday in reaction to a surprise cut in interest rates by the European Central Bank.
The Bank also launched a programme to buy private sector debt, in another effort to boost European economies.
The pound was down 0.10% against the dollar at $1.6314.
The joint administrators of Bradford Bulls have extended the deadline to buy the club to Monday, 19 December.
[NEXT_CONCEPT]
Four men have been charged in connection with a robbery at a Lancashire petrol station.
[NEXT_CONCEPT]
Grimsby Town have signed former York City midfielder Anthony Straker on a deal until the end of the season.
[NEXT_CONCEPT]
(Close): The FTSE 100 index of leading blue-chip shares closed the day down by 0.36% at 6853.40.