Although about 10,000 tickets are still available, a spokesman for the show at the Millennium Stadium told the BBC he is confident it will be sold out.
"I'm excited about tomorrow's event, especially with ticket sales going so well," Chris Hunt, head of Global Events Live, told the BBC. "Buzz is really building and some key acts have already been spotted in the city. Doors will open at 4 p.m. tomorrow for what will be a fantastic evening."
Hollywood actor Jamie Foxx is to serve as host of the "Michael Forever" show.