The Argentine, Inter's leading scorer for the last four seasons, was relieved of the captaincy on Feb. 13 after becoming embroiled in protracted negotiations over the renewal of his contract.
Shortly afterwards, he said he could not play because of a knee injury.
"Considering that so much has happened in this period, including yesterday, I maintain that for this match he cannot be available to help his team mates," Spalletti told reporters.
"He has not been selected for tomorrow's match."
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Spalletti said that Icardi had been absent for so long that it was "like having a new player with us."
He would not commit himself to a date for Icardi's return.
"I have to consider everything that happened, from his last match until yesterday," he said. "He trained with us all week, there are new things that have happened to be evaluated. But training will be fundamental."
Hosts Inter are third in Serie A with 53 points while Lazio are sixth with 45.
(Writing by Brian Homewood; Editing by Christian Radnedge)
