Icardi has scored 29 goals in all competitions this season, and the Argentine forward has attracted interest from Champions League victors Real Madrid.
The former Sampdoria striker has a £96.3m release clause in his contract, and Spalletti admitted that he would not be able to block a transfer if a club were to launch a bid.
"I've spoken with Mauro several times and he sent very precise signals," Spalletti told Sky in Italy.
"He's happy at Inter and wants to stay, but then there are clubs which, if they decide to take a player, you could have been saying 'I won't leave here the day before, then the next day they take you and in the end you're happy to go, even though the previous day you were thinking very differently.
"We have to be ready for anything, but for now there are no signals and no doubts about what he wants."
Icardi will not feature in Jorge Sampaoli's Argentina squad for the World Cup this summer.