Boca Juniors coach Alfio Basile resigned on Friday following his team's humiliating 3-1 defeat by bitter rivals River Plate in a summer-recess friendly.
"A man who has done a lot for the club has just resigned and (reserve team coach) Abel Alves is taking interim charge," Boca president Jorge Amor Ameal told a news conference.
"He decided to distance himself from this institution. We will continue working hard. The players are very upset. I'm surprised he resigned."
Basile, whose side fell to River in Mar del Plata on Wednesday, was unable to build a successful team in his second spell at Boca since his return last July having lifted several titles with the club between 2005 and 2006.
It is the second failed comeback for the 66-year-old after he flopped with the national team in his 2006-2008 spell having steered Argentina to successive Copa America victories in 1991 and 1993.
"We're going to take the necessary time to make a decision (on a new appointment). Alves is a man of the club," said Amor Ameal, referring to the 51-year-old former Boca midfielder, who has been caretaker twice before.
Amor Ameal denied categorically that general manager Carlos Bianchi would be first choice to succeed Basile, saying "Bianchi does not want to coach."
Boca, like River, had a troubled 2009. It will be the first time in 15 years that neither of the country's "big two" will take part in the Libertadores Cup, South America's top club championship.