NRL-bound 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.

On a short playing stint with Panasonic Wild Knights in Japan's rugby union Top League, All Blacks centre Williams was taken to hospital after injuring his right shoulder in a match against Kintetsu Liners in Ota, near Tokyo, today.

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.

Williams is expected to return to rugby league with the Sydney Roosters in the 2013 NRL season.

A part-time boxer, he is the New Zealand heavyweight champion and is scheduled to take on veteran Botha, 44, a four-time world title challenger, in Brisbane on November 24 in his sixth pro bout.

Williams, who is on a contract to play 12 matches for Panasonic reportedly for $1.2 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.

He left the field and Panasonic went on to beat Kintetsu 23-20 for their fifth win against three losses.

Panasonic stood fifth in the league table while defending champions Suntory Sungoliath are top.

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