The midfielder was left out by Cotterill for the weekend trip to Brighton where the visitors produced a solid away display marred by an injury-time winner for the Seagulls.
Cotterill told the Evening Post: "What you have to be mindful of, when you are one of those creative players is, if you are not having a good day – make sure your opponent that you are up against does not have a good day either," but he also added a word of praise for the player.
"I have great faith in the young man. He is that creative player for us. That is why I pick him."
And McGugan looks to have responded well to his manager's urgings, netting in Tuesday afternoon's reserve team clash against Walsall where he was one of a number of senior players to take part.
Andy Reid, Dexter Blackstock (who also netted), George Boateng and Matt Derbyshire lined up alongside trialist winger Aaron Rhule.
Leicester City meanwhile are looking forward to January's 3rd Round FA Cup tie at the City Ground.
"It is a derby game and a good chance to go there and put one over the local rivals," said assistant manager Craig Shakespeare.