The period without their talisman may still be a brief one as the club is working on securing a further loan period before the August 17 deadline.
Villarreal have announced that he does not figure in their plans and no other European club has come forward.
But, at least for Sunday's home game against Rosario Central, Boca will have to do without him.
"There isn't a player who can replace him," said striker Martin Palermo.
"We will have to work harder."
Boca are seen as the main challengers to domestic champions San Lorenzo, who begin their title defence away to Newell's Old Boys the same day.
Ramon Diaz's team have brought striker Bernardo Romeo back to Argentina after his stint with Osasuna in Spain, and midfielder Daniel Bilos from Mexico's America has also been added to the squad.
The season kicks off on Friday with Colon hosting Velez Sarsfield and Banfield facing Diego Simeone's Estudiantes de La Plata, who won last year's Apertura.
The early pressure is on River Plate and their coach Daniel Passarella after a miserable first half to the year which included a group stage elimination in the Libertadores Cup.
River have not won a title for six seasons, considered an eternity for a club which traditionally dominates the Argentine game alongside arch-rivals Boca Juniors.
The Argentine Football Association (AFA) have also announced new restrictions on travelling fans in a fresh attempt to curb violence.
Clubs will be allowed to use only 50 per cent of the capacity of the away fans' sections unless these are all-seater, the AFA announced.