That goal - and the enforced absence of Roy, Jason Lee and Andrea Silenzi - secured McGregor his first Premiership start against Manchester United on Monday, the youngster again scoring in the 1-1 draw.
McGregor admitted that the past seven days - in which he has emerged from anonymity to acclaim at the City Ground - was difficult to come to terms with. "When I came off the bench and got the goal against Lyon last week, that was something of a dream come true for me," McGregor said.
"But to start against Manchester United and score a goal was just absolutely fantastic, the best one of all. It's all a bit much to take in to be honest. I might seem level-headed but that's probably because it hasn't really sunk in."
McGregor's display against United said much for his composure, and the Liverpool-born former Forest schoolboy lacks nothing in confidence. "You've got to be confident in your own ability without being big-headed," he said. "It's no good shouting that you're going to do this, or do that, but you've got to tell yourself you are the best on the pitch, that you will go out there and do the business.
"I played a dozen games or so last season but when the club brought in players like Kevin Campbell and Andrea in the summer I maybe thought a little bit that it was moving me down the pecking order. I'm still a young lad though. The players that were brought in were always going to strengthen the squad but you've got to have the confidence to say to yourself 'I'm better than them.' When you get the chance you've got to go out there and try and prove it.
"Whether the gaffer's going to keep me there is a different story but as long as I keep scoring it will make it harder and harder for him to bring some of the other lads back in."
McGregor is likely to get another chance, at Bolton on Saturday, although Lee could be fit to return at the expense of Stephen Howe after a thigh problem.
"At least the last eight days have reassured us about how bad Jason's injury is," Clark said. "It looked bad when he got it at Blackburn but he was so desperate to play against Lyon that he made a terrific effort before he had to rule himself out.
"You've got to be careful with that sort of injury. If you don't deal with it properly there's a danger of it calcifying, and another knock can be quite bad, but he's improving and has a good chance for Saturday."