Signed from MK Dons on a loan deal last week, the 18-year-old was thrown in at the deep end as Northampton gained an important 2-1 win at Barnet.
"George is here on a youth loan and that can be as long as you want but initially it's just going to be for one month," said Johnson, quoted in the Evening Telegraph.
"It was a difficult game at Barnet and I was pleased with how George handled himself and got through it, I thought he did really well."
Crawley club captain Pablo Mills meanwhile may have put himself into contention for Saturday's televised game at Sixfields after making his reserve team comeback against Peterborough this week.
The defender has been out for six months with an ankle injury.
"It was like he hadn't been away," boss Steve Evans told the club's official website.
"Pablo was excellent for the first 45 minutes and it was mission accomplished in terms of getting him game time."