The All Night Long hitmaker is due to kick off a 35-date trek with Mariah in Baltimore, Maryland on 15 March (17), but sources tell the 67-year-old underwent an operation on an injured knee last month (Jan17) and is still not fully back on his feet.

As a result, he is expected to push back the joint gigs until the summer (17), although representatives for the two musicians have yet to comment on the claims.

The All The Hits Tour was announced in December (16) and had been set to wrap in Fort Lauderdale, Florida on 27 May (17).

Mariah recently revealed she was looking forward to hitting the road with the soul icon.

"I'm honoured because he's a legend and has been doing this for a lot longer than I have. He's awesome," she told St. Louis, Missouri's Fox 2 channel. "I'll be doing my own show; it is about 60 minutes. I'm going to do some hits and fan favourites. It's really going to be for the fans."

The rumoured postponement will give the Hero singer extra down time to spend with her kids, five-year-old twins Moroccan and Monroe, from her marriage to Nick Cannon, and her new boyfriend, backing dancer Bryan Tanaka. The couple has been dating since late last year (16), after Mariah called off her engagement to billionaire businessman James Packer.