The present contract of the Spanish international will expire in less than a year, and according to Il Mattino, Napoli has been attempting to prolong it.
The renowned Italian media outlet has mentioned that Man Utd has submitted an offer that has made the La Roja star push for a move away from the Diego Armando Maradona Stadium outfit.
Ruiz does not intend to discuss the renewal with the Naples-based side, who are now ready to act strongly.
Club president, Aurelio de Laurentiis, has made it clear that a fee of 25 million euros (£20.8million) would be needed to sell the player and if the asking price is not met then the Spaniard will have to sit down and discuss new terms.
If the 26-year-old refuses to sign a new deal, Napoli may decide to leave him out of the squad, which would hurt his chances of participating in the World Cup.
Ruiz is a versatile performer. He can play as a defensive midfielder as well as a creative central midfielder.
Last season, the 15-cap international appeared in 22 games as a CM and 15 games as a DM, contributing directly to 12 goals across all competitions (7 goals and 5 assists).
Man United lost CM Pogba and DM Matic for £0 this summer and must replace the veteran combo.