The 21-year-old midfielder is one of several players being targeted by Roman Abramovich as part of a huge summer spending spree.
Yesterday, Palermo president Maurizio Zamparini told Spanish radio station Cadena Ser: "Chelsea was a club that we had a major offer from for Pastore but it did not reach the minimum figure that we set for a player of his quality.
"If someone wants to buy Pastore, the price is €50 million (£44 million). There are five or six clubs also interested, including Man City and big clubs from Spain and Italy but so far there has been nothing from them."
Pastore scored 11 goals in 35 appearances for Palermo last season.