The Take That singer is looking forward to watching his former bandmate perform on his 15 date European tour next summer, as he will see him restored to his natural environment.
He said: ''Stadiums are where Rob belongs. He is a stadium act. I was down at The O2 [venue in London] last week to see him and thinking how amazing it is that all of us are doing stuff all these years on and at such a high level. I'm so proud of him.''
Gary - who is also a judge on TV show 'The X Factor' - has recently been performing a solo tour across the UK and enjoyed getting back to his roots, singing in more intimate venues.
He added: ''The tour has been brilliant. I feel every night I'm saying, 'That was the best night.'
''It's nice to play live again as it's a good antidote for me from being on TV and just talking to getting out and singing and back to what I do.''
Robbie, 38, rejoined Take That for their 'Progress' album in 2010, before returning to his solo career, but hasn't ruled out reuniting with the band - which also includes Jason Orange, Mark Owen and Howard Donald - in the future.
He said earlier this week: ''We promised each other we would soon meet up for dinner and look through our agendas.
''It would be beautiful if I could do a bit of both [appearing solo and with the group]. This doesn't seem impossible if we can plan it well.''