Longelo is a product of West Ham’s academy set-up and is a regular in their Under-23s squad.
The left-back played the full 90 minutes for the Hammers in their 1-0 loss to Dinamo Zagreb in the Europa League in December and managed to impress at senior level.
Longelo has not been part of David Moyes’ senior squad in any other games so far this season but could be handed an opportunity to play regular first team football, at least for the remainder of the season.
Championship promotion hopefuls Forest are keen on taking the 21-year-old to City Ground this month and have held talks with West Ham over a potential move for him.
Longelo is mulling over whether to leave the London Stadium on a loan deal or on a permanent basis.
Following a poor start to this season, the Tricky Trees are aiming to get into the playoff spots, having got their rhythm back under new boss Steve Cooper and they want Longelo to help them in their chase for promotion back into the top flight.
In addition to Nottingham Forest, the West Ham starlet is also attracting interest from League One.