All Black enforcer Jerome Kaino is in doubt for the British and Irish Lions tour after his Auckland Blues team revealed Thursday he is undergoing surgery on an injured knee.
The Blues said the 77-Test flanker would be sidelined for about six weeks after going under the knife to fix a torn meniscus.
That puts Kaino in line for a return in early- to mid-June.
The Lions are due to pay the Blues on June 7 and their first Test against the All Blacks is June 24.
The two-time World Cup winner's absence would be a massive blow for New Zealand, although Blues assistant coach Steve Jackson insisted it was minor surgery that should not affect Kaino's All Black duties.
"I'm pretty sure he'll be fine for the Lions tour," Jackson told reporters.
"He'll get his feet up and (players) normally come back pretty quick from those sorts of operations."
At the very least, the setback will leave Kaino's preparations severely disrupted, forcing coach Steve Hansen to look at alternatives such as Liam Messam, Elliott Dixon and Liam Squire.