"He's supposed to perform and everyone's really excited," People quoted a source as saying. The 62-year-old superstar knows the soon-to-wed couple through their mutual involvement in charity work.
John performed at the Andy Roddick Foundation's Charity Gala. Last year, Roddick led 'Team Elton John' in the Advanta WTT Smash Hits charity event, which raised more than 400,000 dollars for the Elton John AIDS Foundation.
The wedding to be held in Austin, Texas also has tennis stars Steffi Graf and Andre Agassi, as well as Marty Fish and James Blake on its guest list.