Bell has been identified as a weak link last week by the touring South African coach Mickey Arthur.
It follows claims that Bell rarely scores 'tough' runs for England and his seven Test tons have all come after another batsman has already made three figures, The Sun reported.
The Warwickshire batsman could be dropped when Andrew Flintoff makes his likely England comeback in next week's Second Test.
But Bell said: "I don"t feel under pressure. I'm in control of my game and I want to keep improving. I heard Arthur sees me and Paul Collingwood as weak links at numbers five and six."
"But last week Allan Donald was saying I am the key wicket and England's version of Jacques Kallis. So which one is right? I know I'm a good enough at this level. I certainly believe I can get 20 centuries which puts a batsman in the top bracket," he added.