The 40-year-old singer and X Factor judge admitted that the sheer scale of £15million Progress Tour - which sees the boys reunited on stage with Robbie Williams for the first time since he quit the band in 1995 – is more than a little overwhelming.
He told the Daily Star, 'I try not to think about stuff like that.
'It's a bit daunting if you think, 'Wow, we're going to do Wembley eight times and play to 1.7million people.'
'I only look at what we're doing right now, like a football manager taking one game at a time.
'The success of this tour is already amazing, more than any of us thought we could do.
'I always think, 'It can't get any bigger than this.'
'Maybe it won't, maybe this will be our biggest tour ever, but then I've always been proved wrong.
'It's best not to worry too much about that stuff to stop it overwhelming you.'