Left-footed Johnson has operated on the right of City's midfield and has won praise for his 11 appearances for the Eastlands club.
But he is determined to stay focused, adding: "You've got to keep your feet on he ground and not get too carried away."
With David Beckham and Aaron Lennon injured, Capello has suggested he could hand Johnson his international debut against Mexico on 24 May.
"Johnson has caught my eye," said the Italian. "Now it's important he gets some international experience.
"He has come up from the Championship at Middlesbrough, where he played in a different position, and he has done well with Manchester City."
Sunderland-born Johnson, who came through Middlesbrough's academy, scored his first goal for City in March, a stunning last-minute equaliser against Sunderland at the Stadium of Light.
Capello names his 30-man provisional squad for the World Cup on 16 May ahead of the friendlies against Mexico and Japan on 30 May.
See the full interview with Adam Johnson on Football Focus on BBC1 from 1215 BST this Saturday.
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