HAMILTON, NEW ZEALAND - FEBRUARY 08: Sonny Bill Williams celebrates winning the Battle for the Belt match between Sonny Bill Williams and Clarence Tillman III at Claudelands Event Centre on February 8, 2012 in Hamilton, New Zealand. (Photo by Sandra Mu/Getty Images)

Boxing All Black Sonny Bill Williams said on Tuesday that his heavyweight clash with South African Francois Botha could be in doubt after he picked up an injury playing rugby in Japan.

Williams injured his shoulder playing for Japanese Top League club Panasonic Wild Knights at the weekend and was rushed to hospital for an MRI scan.

New Zealand's heavyweight boxing champion initially said on his Twitter page “results nothing serious, small tear so hopefully still be able to (box).”

But when Williams arrived in Sydney on Tuesday he said his pectoral muscle needed more tests, the results of which could see the Nov. 24 fight with Botha in Brisbane called off.

“At the moment it is a little bit in doubt,” he told reporters at Sydney airport before beginning his preparations to face the 44-year-old Botha.

“I just came back here straight away,” added the 27-year-old. “I've got to get some scans and see how the pec is, see the extent of the injury.”

Williams quit the world champion All Blacks and Waikato Chiefs for a lucrative 12-match deal in Japan worth an estimated $100 000 a game.

He smashed his shoulder into the turf after a tackle in Panasonic's 23-20 win over Kintetsu Liners on Saturday and left the ground with his arm in a sling.

The injury could potentially bring a swift end to the hulking centre's Japanese season, with Panasonic yet to see much of a return halfway through their investment.