Macleod did not play after January last season after being struck by an illness that affected the muscles around his heart.
But the 20-year-old is back to full fitness and his skilful turn took out two Ottawa players before he set up Nicky Law to curl home the only goal of the game.
McCoist told the club's official website: "His confidence is rising and it's like having a new player in many ways. Lewis has had a seriously tough time of it this year with the medical condition he had.
"That was very, very difficult for him and seeing the boys coming in to train each day, especially for a young lad, is soul destroying.
"Lewis handled the situation very well and he has come back looking very strong and he has worked hard in pre-season.
"Without wanting to put any pressure on him at all, if he plays anything like he did for the rest of the season the way he did against Ottawa, we'll be happy."