Sweden boss Jon Dahl Tomasson has suggested that it will take some time for the new Liverpool signing to get up to speed due to his lack of match fitness.
Isak was the centre of a high-profile transfer saga that saw him refuse to play for Newcastle in a bid to force through a move to Liverpool.
The 25-year-old ultimately got his wish on the final day of the transfer window, completing a £125m switch to the Premier League champions.
After putting pen to paper on a six-year deal with Liverpool, Isak linked up with his international teammates for Sweden's two World Cup qualifying games against Slovenia and Kosovo.
Tomasson explains Isak fitness truth
Isak was named on the bench for Friday's clash with Slovenia, but he failed to get on the pitch as Sweden gave up the lead on two occasions in a 2-2 draw.
Speaking after the game, Tomasson admitted it would have been too much of a risk to even use Isak from the bench in Ljubljana.
“We would have loved to play him, everyone would want it," Tomasson told reporters. “But since he only had three training sessions and no pre-season and, of course, no match time, the risk was too great to use him today.”
Isak did not feature in pre-season or any of Newcastle's opening three matches of the campaign, as he stood firm in his desire to complete a switch to Liverpool.
As a result, the Sweden international has not played a competitive game since playing the full duration of Newcastle's final game of the 2024-25 season against Everton.
When could Isak make his return to action?
Sweden will now head to Pristina for Monday's 2026 World Cup qualifier against Kosovo, who lost 4-0 in their opening qualifying match against Switzerland.
Tomasson refused to commit when asked whether Isak could feature on Monday, but he is hopeful that Liverpool's new striker will be able to play a role at some point in the contest.
“Hopefully, hopefully, as a game changer." Tomasson said. But we have to do the right things with him, in the long and short term.”
In truth, the decision whether to use Isak from the bench against Kosovo is likely to depend on the game situation, as well as his fitness levels.
Isak could come on if Sweden are in desperate need of a goal, but he is unlikely to be risked if they are able to establish a comfortable lead.
Meanwhile, he could make his debut for Liverpool when Arne Slot's side resume their Premier League title defence in next Sunday's clash against Burnley.