Midfielder David Havili won’t feature in the Super Rugby Pacific playoffs and is likely to miss the All Blacks’ July tests due to injury.
The 28-year-old Havili limped off in the Crusaders' 42-18 home win over the Waratahs on Saturday.
Robertson, who will take over as All Blacks head coach early next year, said Havili will miss between six and eight weeks.
"I'm sure he can (be fit), it'll only be a matter of weeks (out)," Robertson said of Havili's World Cup prospects.
Havili was added to the Crusaders injury list alongside loose forward Cullen Grace, who suffered a dislocated knee in the same game. Grace won his only New Zealand cap in 2020.
"Both are out for the Super (Rugby) campaign, unfortunately," Robertson said.
"Really disappointed for both of them, they're such big contributors to our team and really important parts of it."