Ramon Diaz has resigned as manager of Oxford United after negotiations over a new contract broke down.
Diaz joined Oxford in December
"Ramon has ended his time as manager and left the country," chairman Firoz Kassam said. "His decision to leave was unexpected and I am disappointed."
Kassam added keeping Diaz would have cost close to £1m and any potential deal was not in the club's "interests".
Oxford hope to keep Diaz's countryman Horacio Rodriguez and Pablo Fernandez on the coaching staff.
Diaz bought the pair in after taking over at the Kassam Stadium from Graham Rix in December.
The 45-year-old, who played 24 times for his country, including the 1982 World Cup, arrived on an initial six-month contract having previously led River Plate to five titles.
His sons, Emiliano and Michael, who were registered as players with United, have also left.