Never have River sunk as low. A 2-1 defeat at home to Lanus on the final day of the Clausura championship was their seventh match without a win.
They now face a play-off for their survival against Nacional B division side Belgrano over two legs away in Cordoba on Wednesday and at the Monumental next Sunday.
"You must all go," the fans chanted at the players as they walked off the pitch under the protection of police shields. "Not one can stay."
"An unidentified fan died in hospital after suffering a heart attack during the match," local media quoted Alberto Crescenti of the emergency medical services as saying.
River are suffering their worst crisis in their 110 years' existence, far worse than the 18 years they went without a title between 1958 and 1975. Many times the record 33 times league champions were runners-up during that bleak period.
River's former captain and coach Daniel Passarella won the presidential election a year and a half ago and has favoured steering a frugal path, refusing to spend on big-name squad reinforcements and betting on ex-team-mate JJ Lopez, a man with poor coaching credentials, to steer the team to safety.
"This is punishment for those who voted for Passarella," said Norberto Alonso, one of River's greatest ever midfielders and a former team mate of the president and Lopez.
By dropping into the relegation zone River have lost their place in the Copa Sudamericana, South America's equivalent of the Europa League, to a team below them in the Clausura standings.
Teams qualify on total points in the season's two championships, the Apertura in which River finished fourth and the Clausura.
