The 31-year-old left-back came in against Kevin Keegan's men for his first start since the visit to Bolton Wanderers last February and handled the dangerous and pacy threat of Shaun Wright-Phillips particularly well while also finding time to get forward and support Trevor Sinclair.
"Scott did exceptionally well against Manchester City at the weekend," says Glenn. "That's his benchmark now and he knows he mustn't drop below that. Hopefully, with a few more games under his belt, he will actually improve on that performance.
"He has waited a long time for this opportunity, because Nigel Winterburn had been in such great form, and he has had to be patient.
"He came to see me quite a lot, telling me he was ready for an opportunity, but with Nigel playing so well it was hard to find a place for Scott.
"I decided to give him his chance against Manchester City and, looking solely at his performance, I think he took that chance.
"He must maintain that level of performance now and, if he does, it will be hard for anyone else to get the shirt off him."
Scott's inclusion at the weekend meant that Nigel Winterburn had to settle for a place on the substitutes' bench, but Glenn insists that the veteran defender will respond to the situation in typical fashion and bounce back to play his part this season.
"Nigel has got a fantastic attitude - if every footballer had his attitude then the job would be a lot easier," he says.
"He's got more medals than most players ever get in a career and you don't become a winner like that unless, one, you are a special player and, two, you are a special person. Nigel is both of those and he is a fantastic example to every young player.
"I just felt I wanted to make a change and bring Scott in, but Nigel took it well and I am certain as I can be that he has still got an important part to play in the team this season."
The Hammers boss takes his side to Stamford Bridge on Saturday to face a Chelsea side high in confidence and form, but says the Hammers are fully prepared for the task ahead, determined to secure that elusive first win of the new campaign.
"It's another exciting London derby and a game that the players are all looking forward to," he declares.
"We know Chelsea well, having played against them four times last season. We won at home in the league, lost at their place in the league and then drew there in the FA Cup before losing the replay back at Upton Park in the last minute.
"With the exception of the league game at Stamford Bridge, we gave a good account of ourselves and we need to do that again on Saturday.
"Chelsea have started the season in spectacular fashion, they are one of only three teams who are still unbeaten, and there probably won't be too many people outside our dressing-room who believe we can achieve a result.
"We have belief, though, and we are all looking forward to the game, confident that we can pull off a result."