"I think there's always a risk," Hammett said, when asked about resting players. Barrett had been earmarked for a stint on the bench three weeks ago until Pisi strained a calf.
There will be nervousness among the Highlanders as they consider the match against competition leaders the Bulls in Dunedin. The South African team, who aren't known for their away form, caused an upset in beating the Waratahs in Sydney last weekend despite chasing the game for long periods.
A win for Jamie Joseph's men is important given they have lost their last two, against the Hurricanes in Dunedin last weekend and the Sharks in Durban before that.
Highlanders wing Hosea Gear has no doubts about what tactics the Bulls will employ on Saturday - lots of kicking.
"They are pretty physical and use the ball a lot. And they will use quite a lot of high balls. Hopefully we have got the game plan to take them on.
"Things might change out on the field and it depends on what sort of picture they want to paint for us. But they are one of teams in the competition which kick the most and they bring up quite a good defensive line so we will just look to hang on to the ball."
The Crusaders meet the Blues in Christchurch on Saturday night following a reversal of recent fortunes, Todd Blackadder's men losing to the lowly Rebels last weekend and Pat Lam's team beating the Lions.
The weather forecast is for cold southerlies and that's the sort of welcome the Blues will be expecting from the crowd as well as the Crusaders look to put things right.
Richie McCaw moves to No8 in the absence of the injured Kieran Read and Luke Whitelock, with Dan Carter moving to first-five and Ryan Crotty to second-five. Tom Taylor, who has begun the last five games at first-five, has been ruled out with a quadriceps injury.
"We're still at the point in the season where we are still in the hunt, this weekend and the one after, they're critical, whether you stay in the game or you start chasing things," said McCaw.
Next weekend the Crusaders have a bye, and play the Highlanders in Christchurch the following week.
The Chiefs have the bye this weekend, for which they receive four points. That means they will maintain a buffer of at least seven points over the Crusaders after this weekend.
In another important match this weekend, the Stormers, who narrowly trail the Bulls in the South African conference, host the Waratahs.