The singer has reportedly shed 42 pounds while preparing to tour with the group - whom he recently rejoined after initially quitting in 1995 ' with his trainer even getting him to sing hits while running on the treadmill.
Fitness instructor Nick Hollender told The News Of The World newspaper: ' make him run on the treadmill and sing all his songs without missing a note.
'He has to catch up to bandmates Gary Barlow, Mark Owen, Jason Orange and Howard Donald who have been on tour much more than him and are in.
'He's not going to be left behind and wants to be trim and healthy, instead of feeling like the podgy member.'
Robbie, 36, reportedly reached 203 pounds in recent years while living in Los Angeles, but after marrying actress Ayda Field this summer embarked on the gruelling four-hour a day workout regime to get him in shape for the 'Relight My Fire' group.
Nick added: 'Robbie is now training like a full on athlete. We need to make sure he can perform the dance moves and sing at the same time.'
Take That will tour Europe between May and July next year. The band's album 'Progress' will be released on November 22.