The future of Chiefs Super Rugby midfielder Charlie Ngatai remains up in the air as he continues to battle the symptoms of a serious concussion.
The one-Test All Black suffered a head knock against the Highlanders in May and has not played a game since then, missing the remainder of the Super Rugby season and the national provincial championship.
Chiefs coach Dave Rennie said the 26-year-old was not back in full training and could miss the entire competition.
"It's been an incredible slow process and he's had a few set backs over the last period of time," Rennie said.
"There's a bit of light at the end of the tunnel but it may get to that stage when we have to make a call but we're going to give Charlie all the time we can.
"Richie McCaw went through this when he was out for a 12 month period so his health is the most important here so we are not going to rush it," Rennie said.
Tasman midfielder Alex Nankivell has been called into the squad as cover should Ngatai be ruled out, while the return of Tim Nanai-Williams from Japan provides another option.