SINGAPORE- Having just made his comeback from a knee injury in Hong Kong, New Zealand rugby star Sonny Bill Williams is eager to get on the field for this weekend's Singapore Sevens Series.

"I'm loving the challenge of sevens rugby so far," he said. "I'm really enjoying it and I'm really happy with how I'm playing and where I am at this stage."

The 30-year-old centre was speaking on Thursday after the All Blacks Sevens' first training session at Anglo Chinese School (Independent) ahead of this weekend's tournament.

The gruelling schedule of playing back-to-back tournaments will be made even tougher for Williams, who returned to the squad in Hong Kong after missing the Las Vegas and Vancouver tournaments.

"It's pretty tough to play just a week after Hong Kong, especially as it is a three-day tournament," he said. "Sometimes it's a mental challenge, not just a physical challenge. With the load of sevens, playing one week and having to rock up again the next week, my body is just adapting to it."

Williams is not the only All Black to suffer from injury problems. The team has five players, including captain Tim Mikkelson, sitting out this weekend's tournament.

Coach Gordon Tietjens acknowledged the demanding nature of rugby sevens. His side are in Pool B with France, Canada and the United States.

"We were really challenged in Hong Kong, we were down to ten men after the first day. Hence the light training week," he said. "There's a lot of pressure on me to share the workload. Every player has got to step up."

"Today was our first training run to bring the younger guys into it. We'll head out tomorrow with a bit more intensity and then look to hit the ground running against France on Saturday."

The All Blacks are second in the HSBC World Rugby Sevens Series with 123 points, five behind defending champions Fiji, who beat them in the Cup final in Hong Kong last week.