Sancho last played in the 1-1 draw with Chelsea in October and Erik ten Hag said the 22-year-old has been out with “physical and mental issues”.
But Sancho returning to first-team training last week and could return after a three-month absence.
“He is training with the team and we will see,” said Ten Hag. ”He is improving, he is making steps, we will make the decision after the training.
“He’s on the way back, he’s making steps, so he’s back in team training and now we have to see when he is ready to go back into the games.”
Ten Hag has confirmed United will name a “strong” side.
The fourth-round clash falls in the middle of their Carabao Cup semi-final tie against Nottingham Forest, but a 3-0 win at the City Ground means Ten Hag may opt for rotation in the upcoming second leg rather than against Reading.
Harry Maguire could be given a rare start as he returns from suspension, while Jack Butland will be hoping to make his debut in goal should Ten Hag opt to rest David de Gea.
Diogo Dalot is definitely out with injury so Aaron Wan-Bissaka will continue at right-back, while Luke Shaw is a doubt and unlikely to be risked. Tyrell Malacia is expected to keep his place.
Both Christian Eriksen and Casemiro might be rested but Marcus Rashford, looking to score at Old Trafford for the tenth match in a row, could start. He was brought off before the hour-mark against Forest, suggesting there’s a strong chance he will be involved from the off against Reading.
There should be a place in the side for Alejandro Garnacho, while the likes of Facundo Pellistri and Anthony Elanga will hope to feature at some point.
Predicted Man United XI (4-2-3-1): Butland; Wan-Bissaka, Lindelof, Maguire, Malacia; McTominay, Fred; Garnacho, Fernandes, Rashford; Weghorst
