The former captain hasn’t played since early February amid talks over a new contract, but the 26-year-old returned to first-team training with the San Siro club during the international break and was expected to start on Sunday.
It was believed that talks had taken place within the Inter hierarchy that would lead to Icardi once again being considered for selection.
He was stripped of the captaincy at the start of last month and has not been involved in any of Inter’s nine matches in all competitions.
Spalletti told Sky Italia: "How he behaved he must stay out. Events are there for all to see, I think he could have played also 45 minutes, but now it is right for others to play.
“There is credibility and being inside the locker room. Messi makes the difference, Cristiano Ronaldo makes the difference, and then at these levels there are few others.
“The discipline is the true strength of a professional.”
Though Icardi is braced to return to the Inter team at some stage before the end of the season, his future beyond the summer is likely to be elsewhere.
Inter chief executive Giuseppe Marotta told Sky Sport Italia: "The reintegration of Icardi is taking place gradually.
"The coach has the right to choose who he works with and who is selected.
"The club always needs to hold a position of leadership and Spalletti has always worked in this way, thinking about the good of Inter."
Serie A champions Juventus, 13-time Champions League winners Real Madrid and Premier League giants Chelsea - despite their looming transfer ban - are among the clubs reported to be keen on taking advantage of the situation.