The 42-year-old 'Take That' singer recorded a track with The 'Rocket Man' last month in New York City, reported Daily Mirror.
"Gary and Elton had a really good time recording the track together. Their voices really complement each other," a source said.
"Now Gary and his label team are busy fine-tuning details on the album between now and the beginning of October, before his 'X Factor' judging duties really kick in with the live shows. The track's production isn't quite finished yet, but everyone's really excited about the vocals," the source added.