Reports in Spain have linked the former Valencia playmaker with a move to the Vicente Calderon despite Jose Mourinho insisting that the 25-year-old will not be sold
Radio Marca reported on Sunday that Atletico were exploring the possibility of a loan move for the Spain international, with the Blues set to complete a deal for Anzhi Makhachkala star Willian to add to a squad that already boasts the likes of Oscar, Eden Hazard, Andre Schurrle and Kevin De Bruyne.
Jose Mourinho insisted on Friday that the 25-year-old former Valencia playmaker would not be leaving Stamford Bridge although Simeone has refused to deny he is interested in a move for Mata.
He told the press after watching his side demolish Rayo Vallecano 5-0 on Sunday: "You [the media] are very wise. You know a lot of things, things that I don't know.
"These last days [of the transfer window] are days with a lot of transfers and we expect them not to be players going out."
Mata was an unused substitute in Chelsea's 2-0 win over Hull City Tigers in their opening fixture of the new Premier League campaign, before playing 65 minutes of his side's 2-1 victory over Aston Villa on Wednesday.