The forward is now just 2/1 to leave Arsenal with contract talks stalling and the Gunners hitting a poor run of form.
Former City boss Manuel Pellegrini last week admitted he wanted to sign Sanchez when he was at the Etihad.
“Alexis Sanchez was one of the best in the world and he showed it every day”
But Sanchez left Barcelona in 2014 to join Arsenal instead as the move broke down over money.
Pellegrini said: “He was one of the best in the world and he showed it every day.
“He was a major player we wanted to take to City.
“We could not take him before he signed for Arsenal, it was because the club was punished for Financial Fair Play.”
Fellow contract rebel Mesut Ozil is 7/4 to move on at the end of the season with 8/1 offered for both Sanchez and Ozil to leave next summer.
Both are out of contract in June 2018 and boss Arsene Wenger insists he’d rather they leave on a free than sell up before then.
Ladbrokes spokesman Alex Apati said: “The Gunners are misfiring, and the latest odds suggest their two main men are edging ever closer to an Emirates exit.”