Together with bandmates Mark Owen and Howard Donald, the 47-year-old was due to go on a global arena tour beginning in April, with dates planned in Australia and South America.
But the group will instead remain in Europe so Gary can stay close to home in order to support an unnamed loved one who has fallen ill.
He told the Daily Mirror: “We had a big ambition next year to do a world tour, but I have actually got an illness in my family and it means I am not going to travel for the next two years extensively.
“So all the plans for South America and Australia that were coming off…
“I thank my two band mates who have been so very understanding, but I just have to be at home – I cannot leave.
“I didn’t want people getting frustrated that we’re not getting out there. I’m a little stuck at the moment, so please be understanding.”
Gary will spend time next year writing a film with Sir Tim Rice, the revered lyricists who penned musicals including ‘Joseph And The Amazing Technicolor Dreamcoat’, ‘Jesus Christ Superstar’, and ‘Evita’.
The news comes after former Take That member and ‘X Factor’ judge Robbie Williams revealed his plans to join the band on tour.
Speaking earlier this month, Williams also said he wanted to try to bring former band mate Jason Orange on board.
He told Magic Radio: “As long as we stay healthy, I’m sure there’ll be another moment where we all get together. Maybe we can coax Jason back, who knows?
“We shall have to see. But definitely, definitely in the future. We will all ride again. Next year when the boys are on tour, I’m on tour too.”