One of Brazil's biggest derby matches was canceled shortly before kick-off on Saturday, after players from Gremio were hurt when fans attacked their team bus on the way to a game against city rivals Internacional.

The match between the two main clubs in Porto Alegre is known as the Grenal but Gremio withdrew from the match at Inter's Beira-Rio stadium after rocks smashed through coach windows and hurt players.

Gremio posted a picture of midfielder Mathias Villasanti being taken to hospital in an ambulance. It also showed photographs of smashed windows and a rock bigger than a fist it said hit the Paraguayan player.

"After the cowardly and absurd aggression suffered by our delegation we have told the Gaucha Football Federation of our decision not to go ahead with the Grenal derby this Saturday," Gremio said.

"In addition to the technical imbalance and the absence of sporting atmosphere this criminal act causes, Gremio's decision also shows our repudiation of all kinds of violence."

Internacional also said it repudiated the violence, adding that two suspects had been arrested.

Gremio later said Villasanti, 25, was being treated for cerebral concussion and cranial trauma. He was also being treated for lacerations to the face and trauma in his hip and would spent the night in hospital for further observation.

No fractures were reported.

It was the second time in three days that a bus carrying a Brazilian team had been attacked on its way to a game, after Bahia players were hit before Thursday night's match against Sampaio Correa in Salvador.

The Porto Alegre incident also took place the same night that fans wielding metal bars invaded the pitch and attacked Parana players, forcing the suspension of their game against Uniao Beltrao in Curitiba.

With around five minutes to go in the state championship match, Parana were losing 3-1, a result that doomed them to relegation to the second division.

Videos showed angry fans punching players, who responded with kung fu kicks as other supporters poured on to the field to join the fighting.

Both sets of players eventually managed to sprint to the dressing rooms as police fired percussion grenades and forced fans off the pitch.