The Croatian winger is known to be high on the wanted list of United boss Jose Mourinho, who has been chasing a deal all summer, but the two parties have so far been unable to agree on a fee.
United are expected to continue their pursuit of the player right up until the close of the transfer window at the end of the month in the hope of wrapping up a deal, but as far as Spalletti is concerned, they will be wasting their time.
Speaking after Inter beat Real Betis 1-0 in a friendly on Saturday, Spalletti told Sky Sports Italia: "Perisic is determined to remain. He spoke like a player who wants to do well and be professional."
The 28-year-old has so far refused to come out publicly and rule out a move to Old Trafford and, until he does, Mourinho will still hold out hope of completing a deal for the player.
United will have to pay a fee in the region of £50million to land Perisic, but reports claim they have yet to meet that valuation.