Maja had looked promising over pre-season, but he picked up an injury early on in the campaign.
The youngster’s progress was blocked due to his fitness problems, but Grayson has high hopes for the forward now he is back in training.
"[Josh] is back training with us now,” the Sunderland boss said.
“It was a big blow for the lad, he'd waited patiently for his opportunity, worked hard in pre-season, looked very good, strong and powerful.
“It was a big blow for us a team when we looking short at the top end of the pitch and for him as a person. When he's back there'll be great competition, I'll be able to look at my bench and have players who I can say, go and change the game.”
Maja’s return is a timely one for Sunderland, as they are in dire need of an injection of quality up-front.
Sunderland are low on options in forward areas, with Lewis Grabban currently sidelined with injury.
James Vaughan has led the line for Sunderland, but his efforts have not been converted in to goals.
Vaughan has found the back of the net just once for the Black Cats so far, and he already is being put under pressure by sections of the Stadium of Light crowd.
Maja, meanwhile, would surely be given time to impress - if he is handed a first-team chance by Grayson.
Sunderland are next in action after the international break, when they take on Queens Park Rangers.