And a video has emerged showing the scenes from inside Boca's dressing room and it's very distressing.
Shortly after 9pm GMT, a letter attributed to South American Football Confederation doctors was issued, declaring that there is no medical reason to postpone the game.
However, it does now seem likely that the match will be suspended and take place at a later date.
This caused the windows of the coach to smash, and meant that when the police attempted to control the crowds by firing tear gas and using pepper spray, which began to affect the Boca players.
River was given a bye into the quarterfinals and Boca was kicked out the competition.
At the behest of CONMEBOL officials, the game was set to go ahead with a simple postponement.
The Boca team bus was held up by River fans as it approached the stadium, with reports from local media suggesting there was limited security outside the ground for the arrival of the away side.
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Lawro has also predicted struggling Newcastle to get 18 points - which would put them in joint eighth place, level with Everton . Oliver Giroud got a late consolation goal for Chelsea , who slipped to their first league defeat under Maurizio Sarri .
"They were throwing pepper gas, stones, everything", the Clarin website quoted Juan Carlos Crespi, a member of the Boca delegation, as saying. Federation Internationale de Football Association boss Gianni Infantino reportedly even told Boca they would be disqualified if they refused to play.
"We are not in a position to play the game, they are forcing us to play the game", said Tevez.
The match between the Buenos Aires rivals on Saturday evening was initially delayed twice after the Boca bus came under attack as it arrived at the stadium.
The tie is evenly poised following an entertaining 2-2 draw in the first leg at Boca's stadium, La Bombonera, last week.
Pictures showed players Carlos Tevez, Pablo Perez, Nahitan Nandez, Dario Benedetto, Mauro Zarate, Ramon Abila and Agustin Almendra among the injured, with captain Perez taken to hospital after being cut by shards of glass.
There will be no Boca fans at the second leg as travelling support has been banned at all Argentine football matches since 2013 due to hooliganism.