Belgian midfielder Nainggolan has been quoted as saying that he has an offer from Southampton to consider, but is holding out for a more high-profile switch.
He has refused to rule out a transfer to England, but feels he should be setting his sights higher than the Saints.
Astori, meanwhile, is said to be interesting Tottenham Hotspur, with Andre Villas-Boas reportedly looking to the Italy international to bolster his centre-half options.
Cagliari, though, insist they have no plans to enter into sale discussions.
President Massimo Cellino told Radio Goal: "I am fed up with nurturing players and then selling them.
"I think that no important players will be sold and would prefer to see the team reinforced."