Arsenal boss Arsene Wenger has expressed his confidence that Sanchez and Mesut Ozil will commit their future to the Emirates.
But Pires has added fresh doubt to the situation by revealing the details of a discussion the pair had.
PA
Alexis Sanchez celebrates his late winner against Burnley
The Frenchman, who played for Arsenal between 2000-2006, told Chilean outlet La Tercera: “I spoke to Alexis last week and asked about the renewal.
“He told me he didn’t know, that he only cared to play. The renewal is not a subject for Alexis.
“He doesn’t know what is going to happen, he just wants to play and enjoy.”
Reuters
Alexis Sanchez's contract has less than 18 months to go
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Nevertheless, Pires remains hopeful Sanchez will stay at Arsenal.
He said: “All we want is for Alexis to remain at Arsenal. I hope he renews his contract because he is a wonderful player.
“Alexis is the engine of the car. I hope he stays forever.”