Former All Blacks centre Sonny Bill Williams is confident that he will be fit to fight South African Francois Botha in a heavyweight boxing match next month after suffering a shoulder injury.

Williams, on a short stint to play for Panasonic Wild Knights in Japan's rugby union Top League, was taken to hospital after injuring his right shoulder in a match against Kintetsu Liners in Ota, near Tokyo, on Saturday.

"Hurt today .. results back nothing serious, small tear so hopefully still be able to (fight Botha)," the 27-year-old part-time boxer wrote on Twitter hours later.

His first tweet after sustaining the injury said: "Going in for MRI hopefully just a small tear?!!"

It was accompanied by a picture showing his right arm in a sling and his left hand clenched as if he was ready to fight. What appeared to be a Japanese hospital worker in white stood next to him flashing a right fist.

Williams, the New Zealand heavyweight champion, is set to take on veteran Botha, 44, a four-time world title challenger, in Brisbane on November 24 in his sixth boxing match.

Williams, who is on a contract to play 12 matches for Panasonic reportedly for __?__.2 million, scored a first-minute try, his second since joining the team, in the Top League eighth round.

But he crunched his shoulder attempting a tackle on former Western Force centre Gene Fairbanks 10 minutes into the match.

The New Zealander was taken away from the field and Panasonic went on to beat Kintetsu 23-20 for their fifth win against three losses. Panasonic stda fifth in the league table. Defending champions Suntory Sungoliath are top.

The Top League went into a five-week break with its final set for late January.

Williams is expected to return to Australia's National Rugby League in the 2013 season, possibly playing for the Sydney Roosters.

AFP