A number of clubs are chasing the 32-year-old, but Transfer Nexus understands that Betis and Boca are the frontrunners.
It is a difficult decision for Isla with a move to Boca appealing because it would put him just two hours away from his family.
Boca has been Isla’s preferred choice in recent weeks, but a new development could prove decisive.
El Ingeniero arrives
Betis’ appointment of Isla’s countryman, Manuel Pellegrini, as head coach on Thursday may swing things their way.
Pellegrini is a much respected figure in Chile and his presence makes Betis an attractive option for Isla.
Furthermore, after playing in Italy, England, France and Turkey, it would give Isla the chance to experience La Liga.
After several failed attempts, Betis want to build a project that will get them into the UEFA Champions League.
And Isla, a player with experience in Europe from his days at Juventus, would be a crucial signing.
Isla is currently in Spain on holiday and will decide his future very shortly.