After featuring against Manchester United, Johnson joined the England Under-21 squad in Bristol ahead of their Tuesday evening friendly against Romania, reuniting himself with former City boss Stuart Pearce.
Pearce has been credited with helping nurture talent such as Johnson at Eastlands, with Sven-Goran Eriksson arriving in the summer to supplement a talented young squad.
"You can see from nine points out of nine - we've done as well as we can and on Sunday we were playing against one of the best teams in the world which is hard," Johnson said.
"Before that there were already good players at the club. He's added good players to good players.
"To me it's no surprise because we brought in a lot of good players.
"The lads have all gelled really well. There are a lot of nationalities in the dressing room but it's not quiet. Everyone speaks to each other and gets along well."