The Haven't Met You Yet hitmaker became friends with the country star after Shelton released a cover of Buble's song Home in 2008, and they have collaborated on several projects since.
The Canadian crooner has also worked with Williams, recording a duet with the British pop star last year (13), he thinks the three of them would make a good trio.
Buble tells Australia's Sydney Daily Telegraph that Williams is the "greatest entertainer the world" adding, "I love him. I would love to be in a Rat Pack with Robbie and Blake. Robbie is the man. I would like to work with Mr Williams again, I would love to do a show with him."