Macleod capped a fine display against Ottawa Fury when he set up the only goal of the game for team-mate Nicky Law. The Scotland Under-21 star was sidelined for the second half of last season due to a debilitating virus that affected the muscles around his heart.
But he is now back in blue for the Ibrox side and McCoist said: "His confidence is rising and it's like having a new player in many ways."
The midfielder has gone from strength to strength since the SPFL League One champions returned to training at Auchenhowie last month.
The fine performance against Ottawa - when the teenager played for 79 minutes before being replaced by Dean Shiels - had been coming.
He scored a superb goal in a closed-doors game against Fulham at Murray Park shortly before the Glasgow club jetted across the Atlantic.
And since then he has impressed watching Gers supporters in the overseas matches against both Ventura County Fusion and Sacramento Republic.
McCoist has only added four new players to his squad this summer - Kris Boyd, Darren McGregor, Kenny Miller and Marius Zaliukas.
But the Light Blues gaffer has been delighted with the rapid progress Macleod has made since being given the go-ahead by club medical staff to return to action.
However, he stressed he will not rush the player back into action and risk setting back his recovery from the illness that ruled him out last season.
But he has told the talented youngster that he will feature for his team in the second tier if he maintains his high performance levels in the weeks ahead.
Speaking to the official club website, McCoist said: "Lewis has had a 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.
"I wouldn't like to start singling people out because we've had some good, solid performances from a lot of the boys, but Lewis has been bright, as we expect him to be."
Meanwhile, two Rangers matches will be shown live on BT Sport - at Raith Rovers on Friday, September 12 (7.45pm) and at home to Hibernian on Monday, September 29 (7.45pm).