The 25-year old has scored four goals in seven appearances so far this season and McLeish puts it down to the fact that he has been given an opportunity after making just 17 starts under Gerard Houllier last term.
"First and foremost, I think we gave him the opportunity to play," said McLeish.
"Gabby showed some great application from day one at the training ground. I like to see them train the way they play on a Saturday and Gabby right away impressed.
"The other side of it was how best to integrate him with Darren Bent. I am not saying they are the finished article but we have to keep improving and building on it. It has been very promising and Gabby was electrifying at times in the Wigan game."