The 63-year-old performer sung at the funeral of Prince William's mother Diana in 1997 and he recently said he will 'probably' perform at William's wedding to Kate Middleton.
Speaking to Steve Wright on BBC Radio Two, he was asked if he would sing at the wedding and he said: 'I probably am.'
He jokingly added: 'I'll probably be busking outside.'
John will soon be guest-editing an issue of The Independent newspaper but said there won't be much in there about the royal wedding.
He said: 'There's not going to be much about the royal wedding in there, though. I think we've had enough of that for the time being.'