Zenit fans attack Dynamo captain in pitch invasion
Fans of the Zenit football club walk on the field of the Petrovsky stadium during the Russian Premier League match against the Dynamo Moscow in Saint Petersburg on May 11, 2014
Andre Villas-Boas's side were losing 4-2 in the 87th minute when Zenit fans launched their assault and forced the game to be abandoned.
One fan punched Dynamo skipper Vladimir Granat twice in the head. Granat was helped from the field in a daze with reports saying he had suffered concussion.
Dynamo officials said they would launch legal action.
"The attack on Granat is without doubt a criminal offence," the Interfax news agency quoted one senior Dynamo figure as saying.
"I believe that the law-enforcement authorities should investigate this case."
Zenit said the club were trying to identify the fan who attacked Granat.
"The fans' unruly behaviour is a serious blow for the club's reputation," Zenit press service chief Yevgeny Gusev said.
"The club and the police are trying to identify the person who attacked Granat. We're also preparing evidence for launching legal action against him.
"We believe that the persons guilty of this incident will suffer punishment for their actions."
In a statement issued later, Zenit added: "Besides the match itself being stopped due to fan aggression, the most shameful episode came from aggressive fan behavior towards the players of the opposing team.
"Such fan behavior has an enormous negative influence on the reputation of the club, its players, and all of the many millions of Zenit fans.
"Unfortunately, this is not the first time that fan groups have caused damage to Zenit's reputation. This forces the club to change its approach to further interaction with such fan groups.
"We apologize to all of the players and fans."
Zenit now face an automatic 3-0 defeat - which will have a serious impact on their chances of winning the title - and other sanctions.
The head of the Russian Football Union (RFU) disciplinary panel Artur Grigoryants said a decision on the case would be taken on Wednesday.
"We need to collect the documents and to hear the match officials' evidence," Grigoryants was quoted as saying by ITAR-TASS news agency.
The head of the Russian Premier League's security service Alexander Meitin said a new law on fans' behaviour, brought into effect this year, should be used to deal with the incidents.
Under the new law, persistent troublemakers can be banned for up to seven years.
"Now is the right moment to use the new law," Meinit was quoted as saying by the R-Sport agency.
"Those who initiated the incidents should be banned from attending football matches under this law."
- Precedent -
Last season Zenit were handed a 3-0 technical defeat at Dynamo after a firecracker thrown by one of their fans injured Dynamo goalkeeper Anton Shunin.
Zenit were also sentenced to a 1.3 million-rouble ($35,000) fine and ordered to play two Premier League matches behind closed doors and they went on to finish second, two points behind champions CSKA Moscow.
This year's title could again be decided by the punishment, with CSKA moving above Zenit after a 2-0 win against Tomsk and Lokomotiv Moscow also poised to leapfrog Villas-Boas's side with a win at Rostov later on Sunday.
Villas Boas's side had been undefeated in seven league games going into the match and went one up after six minutes, Portuguese midfielder Danny firing in the rebound after Dynamo goalkeeper Vladimir Gabulov deflected Salomon Rondon's close-range shot.
However, Dynamo pulled level in the 35th minute. Artur Yusupov fired the ball home from just inside the penalty area with the help of a ricochet off Zenit's Italian full-back Domenico Criscito.
In the 57th minute Argentinian defender Leandro Fernandez put Dynamo ahead, and Ecuadorian midfielder Christian Noboa's header made it 3-1 eight minutes later.
German forward Kevin Kuranyi scored Dynamo's fourth in the 71st minute before Russian international Alexander Kerzhakov pulled another one back for Zenit.