The 'Candy' singer last toured with the group in 2011, but is not featured on their latest album III, reported Digital Spy.
However, Williams, 40, told fans on Facebook that he will "likely" team up with the group for a future project.
When asked if he may return for Take That's 25th anniversary in 2017, he said: "I'm pretty sure I'll be re-joining Take That. When and where, I don't know."
Gary Barlow also said that Williams and Jason Orange are always welcome in the band.