The midfielder, 24, has had a tumultuous time at Inter since joining in 2015 and skipped Friday's session without notifying the club.
Kondogbia has been heavily linked with a move to Valencia and Spalletti believes he has already received an offer, but insists no agreement has been struck between the clubs.
"Kondogbia had this idea for some time. Evidently someone has made promises to him, but they have to be shared with us," he told reporters before revealing that Jeison Murillo also wants to leave San Siro.
"We will not hold him here with force, neither he nor Murillo, but we need an agreement.
"I have already talked to them recently. I'm a bit surprised because I had made little promises, for me Kondogbia is a strong midfielder, we want to understand what happened."