Slimani, who was in Algeria's squad for their African Nations Cup qualifier against Lesotho earlier this week, scored 27 league goals in 33 appearances as Sporting finished second in the Portuguese championship last season.
"Slimani arrives this evening or tomorrow. I didn't see him yet. He's available for Saturday. He could play. We bought him because we believe in his ability," Ranieri told reporters on Thursday.
"He cost a lot of money but if you see the market it's a crazy market."
Ranieri also said goalkeeper Kasper Schmeichel was ready to return to action after having surgery on a hernia. None of his players had been injured on international duty, he added.
Ranieri, who led 5,000-1 outsiders Leicester to the league title last season, backed Liverpool, who ended last season in eighth place, to challenge for the league title this campaign.
"Liverpool is one of my favourites to win the league," he said.
"They are ready to fight for the title. We go there to try and win. We are the champions. It'll be difficult for us but also for them."
Both teams are on four points in the table, with a win a loss and a draw from their opening three games.
Leicester became the first Premier League champions to lose their season opener when they were beaten 2-1 away at Hull City on Aug.13.
(Reporting by Ian Rodricks in Bengaluru; editing by Clare Lovell)
