The Ivorian midfielder missed last week's 1-0 upset of Liverpool, which he was initially labelled a "doubt" for, but it has now been reported that he is facing a couple of months on the sidelines with a torn hamstring.
Sangare joins fellow midfielder Danilo in the medical bay - the Brazilian will likely be out until 2025 with a fractured ankle - but Willy Boly (calf) has not been ruled out of Sunday's game just yet.
Regardless, Santo will surely not even consider changing the backline that unexpectedly shut out Liverpool last weekend, as Ola Aina, Alex Moreno, Murillo and Nikola Milenkovic shield Matz Sels.
Ryan Yates and James Ward-Prowse are poised to form an unchanged pairing in the Forest engine room, as Morgan Gibbs-White pulls the strings further ahead; the England international has created the most chances from open play of any Premier League player this season (11).
Callum Hudson-Odoi and Anthony Elanga were both forced to make do with second-half cameos against Liverpool last weekend, but the former's sublime winner off the bench will surely earn him a recall over Elliot Anderson.
Elanga has every chance of coming in for Nicolas Dominguez too, as Santo reverts to a bit more of an attacking shape, while Chris Wood continues to keep Taiwo Awoniyi at bay up front.
Nottingham Forest possible starting lineup:
Sels; Aina, Milenkovic, Murillo, Moreno; Ward-Prowse, Yates; Elanga, Gibbs-White, Hudson-Odoi; Wood