Fellaini suffered a hamstring complaint in February, while Valencia has been out of action since last year having undergone surgery on his foot.
In his pre-match press conference ahead of the game against Watford on Wednesday, van Gaal revealed that the duo have reached the “last step” of their recoveries.
“Fellaini and Valencia are the next ones to come back, I think,” van Gaal said.
“Fellaini shall come into the last step of the process, team training, and also Valencia today has trained with the group, so they are coming back.
With Chris Smalling, Matteo Darmian, Marcos Rojo and Anthony Martial set to return against the Hornets, it’s seems as if United are coming out the other end of the injury crisis they have had to contend with in recent months.
It has come at exactly the right time, with a number of tough fixtures coming up for United. It will be interesting to see if van Gaal drops the likes of Marcus Rashford and Guillermo Varela following their good form as of late.