An attack by rival fans on the Boca Juniors team bus left a number of players injured and forced the postponement of the Copa Libertadores final second-leg.
Players, including ex-Manchester City striker Carlos Tevez, were left with cuts from broken glass and feeling dizzy and nauseous from the effects of tear gas.
Fans attacked the bus as Boca Juniors arrived at River Plate's stadium in Buenos Aires, Argentina, for Saturday evening's match.
Television footage showed River supporters hurling objects at the bus as it made its way to the El Monumental ground.
Police were forced to intervene, using tear gas to disperse the crowds.
Several Boca players were reportedly treated by club doctors for dizziness and vomiting.
Footage apparently from inside the Boca dressing room showed the players groggy and disorientated.
It was reported that Boca's Pablo Perez and Gonzalo Lamardo had been taken by ambulance to hospital, the former with slivers of broken glass in his eyes and the latter a cut on his head.
The bus driver was said to have been knocked unconscious by a rock.
The match was set to kick-off at 8pm GMT, but the start of the game was put back twice, the latter time to 10.15pm.
Eventually CONMEBOL, the South American Football Confederation, postponed the game until Sunday.
Concerns remain for the well-being of the players and it is not certain if the match will be played, however.
General secretary Christian Gribaudo was quoted as saying by the website of Argentinian newspaper Clarin: "The players are all injured, you can't play likes this."
Former Argentina striker Gabriel Batistuta branded the scenes "shameful", saying on Twitter: "Another opportunity lost in front of the whole world that observes us, shameful, lamentable."