The Reds reportedly issued an offer with an evaluation of £10 million for the 23-year old.
But the Terriers are holding out for more as they negotiate a price with the newly promoted Premier League side.
The terms of Forest’s initial offer has not met the structure that the Championship side are looking to reach in order to sanction a sale.
O’Brien had a fixed fee inserted into his contract when he signed a new deal last season, which has not been met by Forest.
Huddersfield are also holding out for a greater percentage sell-on clause than was initially offered.
The club is hoping to earn 20 per cent of any future sale of the midfielder by the Reds.
Forest are also offering unfavourable terms as Huddersfield are hoping to receive more of the payments up front, rather than in instalments.
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While both clubs may be close in their overall valuation of the Englishman, there is still some distance in their understanding of how to structure the deal.
The pair are also still negotiating over the price for full back Harry Toffolo, with more talks expected soon.
Given the relatively small distance in evaluation between the two clubs, it would come as no surprise to see this deal wrapped up soon.
O’Brien was a standout player for the Terriers last season under Carlos Corberan and showed he has the talent to compete at Premier League level.
Forest are building a fun side under Steve Cooper, with the club already adding a number of high profile players as they look to maintain their place in the top flight.
It would come as a huge blow for Huddersfield to lose both O’Brien and Toffolo, especially given the shock departure of Corberan last week.