Roberto Firmino, Alisson and Fabinho have linked up with their teammates after taking an extended break following Copa America.
And Klopp says the three players could be thrown straight into the action against the Serie A side.
"The players who play international football never have enough time; that was always like this," he said.
"You never have enough time to train and stuff like this – a week, two weeks before the season.
"[The Brazilian players] will start tomorrow with training properly with us.
"Maybe on Thursday in our two 60-minute games against Bologna, we can involve them already. I don't know yet – maybe 15, 20, 30 minutes. We have to see how they look exactly."
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