Steve Cooper's side defeated the Terriers in the Championship playoff final back on May 29, courtesy of a Levi Colwill own goal in a 1-0 victory, which ended their 23-year wait for a return to the Premier League.
Both O'Brien and Toffolo were part of the Huddersfield side at Wembley Stadium that day, but although the duo missed out on an exceptional achievement of reaching the top flight with the Yorkshire outfit, they could still be plying their trade there this year.
That is according to a report from The Athletic, who are reporting that the Reds have made a combined offer of between £10m and £12m for the pair ahead of the 2022-23 campaign.
However, it is suggested that Huddersfield value O'Brien himself at around £12m, meaning that the bid is unlikely to be successful at this stage.
The 23-year-old was one of the standout performers in the Town side that arguably overachieved in reaching the playoffs last season, during which he made 43 league appearances largely from central midfield.
On the other hand, Toffolo also enjoyed an impressive campaign in a left wing-back role, scoring six goals and registering seven assists in 42 Championship matches.
With the 26-year-old entering the final year of his contract, his valuation is said to be much lower than that of O'Brien's - rumoured to be around £2.5m - and although Huddersfield are keen to retain both players, the report suggests that the club will not stand in their way should they decide to pursue a move to the Premier League.
Ahead of their long-awaited return to the top flight, Forest have made six signings already this summer, bringing in Taiwo Awoniyi, Neco Williams, Omar Richards, Moussa Niakhate, Giulian Biancone and Dean Henderson so far.