Inter Milan are in talks with Newcastle United's Moussa Sissoko over a move to the San Siro.
Sissoko wants to leave St James's Park before the transfer window closes at the end of the month.
And the midfielder's representatives are understood to have held informal discussions with the Italian club.
Newcastle, however, are yet to receive a formal approach for the £35million-rated France international, who has not played for the club so far this season.
Inter manager de Boer, also considering a move for him and Sporting Lisbon's Joao Mario, said this week that the 27-year-old was an "interesting player".
De Boer said: "We need a strong team, and perhaps it's true that our midfield is not complete yet at the moment.
"We will have to keep a close eye on what happens on the transfer market. Joao Mario and Sissoko are interesting players."
United manager Rafa Benitez has stressed in recent weeks for Sissoko's suitors to table bids well before the transfer deadline.
And Benitez said again this week that he would be "happy" for Sissoko to stay at the Championship club, which does NOT need to sell him.
Sissoko angered Newcastle earlier this month with a series of interviews in which he reiterated his determination to leave in the wake of relegation.