After sitting out three group matches with a calf injury, Australia's talismanic captain came off the bench late in the 2-0 win over Denmark, raising home fans' hopes of a bigger role for her against France at Brisbane's Lang Park.
Barring a surprise 3-2 loss to Nigeria, Australia have coped well without their star striker, netting six goals in their last two matches.
But Gustavsson said he had no fears about upsetting the Matildas' momentum by using Kerr from kick-off.
"I definitely would never ever see Sam as a disturbance to the team," the Swede told a press conference on Friday.
"And I want to be very clear here and now to say if Sam is fit to play 90 minutes, she is starting. That's not even a question, and the team knows it.
"We're talking about Sam Kerr. Whether she is ready to play 90 minutes plus extra time, that's to be decided tonight."
Gustavsson had all of his squad training at their last session, including striker Kyah Simon, who has carried a long-term knee injury into the tournament and not played a minute.
Simon's availability will also be assessed by medical staff later on Friday, Gustavsson said.
Having never made the semi-finals at a World Cup, Australia will break new ground if they beat France.
France were knocked out of the quarter-finals as hosts of the 2019 tournament by a champion United States team that featured Gustavsson as an assistant to then-coach Jill Ellis.
France manager Herve Renard remarked this week that the pressure will be on Australia as co-hosts on Saturday.
The match will draw a capacity crowd to Lang Park and be broadcast live on free-to-air TV, coast-to-coast.
Thousands of fans will flock to live sites in Australia's major cities, while crowds going to watch Australian Rules football matches in Sydney and Melbourne will be able to watch the Matildas on big screens at the stadiums.
Australia defender Ellie Carpenter said the nation's support was a motivation for the Matildas rather than pressure.
France, however, would see their campaign as a failure if eliminated on Saturday, the Lyon fullback added.
"Their mentality is if they're out at a quarter-final, that's not good enough for them," she said.
"They're going to be confident tomorrow. Of course, they're going to come out and show that they are confident. But that doesn't bother us at all."
