* Dynamo defender Vladimir Granat concussed after punch in head by Zenit supporter
* Match abandoned after 87 minutes with Dynamo leading 4-2 (Adds injury detail, Zenit comment)
MOSCOW, May 11 (Reuters) - Zenit St Petersburg's Russian championship clash with Dynamo Moscow was abandoned in the 87th minute on Sunday after Zenit fans invaded the pitch and Dynamo defender Vladimir Granat was punched in the head.
Zenit were losing 4-2 in a match that threatened to dent their title challenge when fans ran on to the field and tried to confront the players.
One managed to get near enough to Granat to swing a punch that connected, despite the Dynamo captain trying to defuse the situation.
After being assessed at a St. Petersburg medical clinic, Dynamo sporting director Guram Adzhoev said Granat, 26, had suffered a concussion.
Speaking to the television channel NTV Plus minutes after the incident, Dynamo head coach Stanislav Cherchesov said: "I would not want to play. If I was hit, would you force me to go back on to the field?
"I would not want to do that. The player was hit in the face a few times and he says I don't want to go back out there. What can you do?"
The referee led the teams off the field and after a meeting with the match delegate, the decision was made to abandon the encounter.
Zenit released an official statement on their website saying fans had the right to be disappointed with the performance of their team in such an important match but that "hooliganism and unrest are inexcusable".
"The behaviour of the fans is affecting in the most serious way their own club, the players and our many millions of supporters," it said.
Zenit apologised to Granat, who was almost certain to be included in Russia's World Cup squad, and said they were going to take action against radical fan groups that have damaged the club's reputation.
"At present the police and the club are trying to find the fan and we are preparing evidence for a criminal case", it added.
Zenit, who have been managed since March by former Tottenham Hotspur and Chelsea boss Andre Villas-Boas, currently lead the standings with 60 points from 28 matches, one point clear of Lokomotiv Moscow in second.
Their opponents Dynamo Moscow, in fourth place with 49 points, are likely to be awarded a 3-0 victory.
Zenit could also be punished by having to play between one and five matches at a neutral venue without their own fans.
In 2012, a Zenit fan threw a flare, which hit Dynamo goalkeeper Anton Shunin. The match was halted immediately and Zenit's opponents later awarded a 3-0 victory. (Reporting by Dmitriy Rogovitskiy; editing by Toby Davis and Josh Reich)