The Owls added 12 players to their squad over the summer, including Scotland international forward Stevie May from St Johnstone.
However, with just eight goals scored so far this season, Gray has been told that he can boost his frontline if he wants to.
"Stuart will keep getting support on and off the field," Mandaric told the Sheffield Star. "Stuart has got the green light to sign another striker to put positive pressure on our forward line.
"Whatever additional improvements Stuart needs to make, we will do that. We will not just get a player in to make up the numbers."
The Championship side return to action tonight when they travel to holders Manchester City in the third round of the League Cup.