The 22-year-old scored his first goal for the club since his £400,000 move from Crystal Palace in June.
Scannell, given the chance of a more attacking role because of injuries to strike duo Jermaine Beckford and James Vaughan, responded to Grayson's faith with the only goal just before half-time.
And the Huddersfield boss was delighted with the winger's display as Town returned to winning ways after back-to-back defeats.
Grayson said: "He can be what he wants to be. We haven't seen the best of him yet but he has shown glimpses of what he is capable of.
"He was a constant threat with his power and pace. He started the season but then got a hamstring injury and when he came back he wasn't able to get back in the side.
"We have worked hard with him on his fitness, which was lacking, and we're also working on his positional play.
"He played really well for the under-21 side against Leicester on Tuesday and that's what earned him his chance."