Astrada's team have taken one point and scored no goals in their last five matches in the Clausura championship after Sunday's 0-0 draw away to bottom team Atletico Tucuman.
River have gone a club record 465 minutes without scoring and are near the bottom of the standings with 13 points from 14 matches.
"Yes, I've been kicked out," Astrada, who had taken charge last October, told reporters as he left the club's Monumental ground on Monday.
"The hardest knock was against Boca. That the match was suspended that Sunday reduced the adrenalin we had and ended up by killing us," he said.
Astrada's team went into last month's "Superclasico" away to arch-rivals Boca Juniors on the back of a 2-0 home win over Huracan that lifted their spirits.
A rainstorm flooded Boca's Bombonera ground and the match was abandoned after nine minutes. Boca won the rescheduled derby 2-0 four days later against a colourless River, sparking their run of defeats.
CAPPA FAVOURITE
River, the team with most league titles in Argentina since the advent of the professional game in 1931, are in a dangerous position in the relegation averages taken over three seasons.
A poor 2010-11 season would push the club that produced Alfredo di Stefano in the early 1950s and an array of more recent talented exiles to top clubs in Europe towards the brink of a first ever relegation.
Club president Daniel Passarella, Argentina's 1978 World Cup-winning captain and a former skipper then coach of the Buenos Aires giants, called a news conference for Tuesday to announce Astrada's successor.
The Spain-based Argentine Angel Cappa, who steered Huracan to second place in last year's Clausura championship on a shoe-string budget playing a passing game in the same tradition as River's, is favourite, the sports daily Ole reported.
The fans' favourite to return as coach is former Inter Milan and Argentina 1982 World Cup striker Ramon Diaz, who steered the club to their second South American Libertadores Cup in 1996 and five league titles in two spells in charge.
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