Gary Madine has been told he must produce strong performances on a consistent basis if he is to win a regular place in the Owls side.
The striker impressed after coming off the bench at half time for Wednesday at Leeds, showing great energy and strong hold-up play.
But head coach has warned Madine he must now show consistency if he is to trouble first-choice strike pairing Stevie May and Atdhe Nuhiu.
“When your subs come on, you want them to make an impact and Gary did that for us at Leeds,” Gray said.
“But he knows and I know that he’s got to do it consistently as well.
“Gary has been patient and all credit to him. He’s shown us what he can do when he gets his chance.
“He also had a great chance at the end and we felt it was going to be the winner for us but it wasn’t meant to be.”
Gray admits he does have some sympathy with the 24-year-old, who he says is not quite up to full match fitness.
Madine has played 163 minutes of league football so far this season though he did start the Owls’ three Capital One Cup ties.
Gray said: “I’ve said this about players you bring in on loan but when lads aren’t playing regularly, then you’re getting them up to match fitness in games.
“Gary is at a decent level of fitness but he’s not got that high intensity fitness from playing week in, week out.
“Saying all that though, I felt I turned the game for us at Leeds.
“We’d struggled for a foothold in the game.
“His ball retention was great and he was more of a physical presence against their centre backs.
“It just gave them something different to think about than what Atdhe did. It allowed us to have more possession in their half.
“I’m not blaming Atdhe – our passing wasn’t good enough, we played the ball square too much which was unusual for us.”
Gray has ruled out a loan move for Madine – even if he was to bring in a temporary signing himself – as he wants to retain as many forward options as possible.