Rio 2016: Sonny Bill Williams upbeat

Sonny Bill Williams' journey with New Zealand at the Olympic Games in Rio may have ended prematurely due to an Achilles injury, but he is remaining upbeat.

Williams was part of the All Blacks side that triumphed at the 2015 Rugby World Cup but switched codes ahead of the inaugural Olympic rugby sevens competition.

The 31-year-old started New Zealand's opening match against Japan on Tuesday but left the field early in the second half through injury.

The All Black Sevens went on to suffer a surprise 14-12 defeat, and the news only got worse with confirmation Williams had suffered a partial Achilles rupture.

Although the injury casts doubt on the New Zealand star's potential participation in the Rugby Championship, he remained in high spirits and is confident the team can still challenge for gold.

"Down but never out, always praise to the most high for blessing me with so much!" said Williams in a post on Twitter.

"Let's go @nz7s we [are] still in this."