Monchi, Roma's new sporting director, has been adamant the club will retain the midfielder but Inter are pursuing the 29-year-old, who hit 11 Serie A goals last season.
Spalletti said Inter are still hopeful a deal can be struck for Nainggolan, who has also been linked with Manchester United and Chelsea, and the Italian is not concerned about the club's lack of transfer activity compared to big-spending arch-rivals AC Milan.
"That is something the directors are working on," Spalletti told reporters after Inter's pre-season friendly defeat to Nurnberg on Saturday.
"As I said, we need to let certain situations mature and Nainggolan is one of them. It has been talked about and the directors are keeping that in mind.
"We've got a good team with many players who haven't expressed themselves to their full potential and those who arrive will help complete the side. We don't need to have an extraordinary transfer market to aspire to the top four.
"I feel reassured in every way. Clearly we had some discussions and when you make a promise, you have to maintain it, so I am confident it'll happen.
"Because those two, three, four players we need to put into the squad don't necessarily have to be top champions, but simply completing the team in those areas that are lacking.