According to a report in The Times, the deal is thought to have been delayed by Si Advisers bringing in a co-investor to help bankroll its bid.
However, the identity of the additional party remains unknown.
Restaurant has contacted The Ivy for comment.
It was reported back in September last year that Si Advisers, a little-known London-based firm, was on the brink of signing a deal with The Ivy owner Richard Caring that would value the group at around £1bn.
Caring launched a £1bn auction for his share in Troia (UK) Restaurants, the parent company of The Ivy Collection, in January last year.
It was subsequently reported in June that Caring was expected to completely cash out of the business, having initially been expected to retain a residual stake in the group of about 25%.
The group, which encompasses The Ivy and The Ivy Asia brands, as well as the London-based Granary Square Brasserie and Brasserie of Light concepts, is understood to have generated £60m in earnings before interest, taxation, depreciation and amortisation in its latest annual results, according to The Times.
Sources familiar with the situation told the publication that the group is bracing for a £6m annual hit from increases in employer National Insurance contributions (NICs), which is set to come into force in April having been announced in the Government’s Autumn Budget last year.
They insisted that the increase to NICs would not blow the sale off course with Caring’s team having identified head office savings and introduced menu increases to compensate for the impact of the tax rise.