LONDON (Reuters) - Russia is worried about possible fan violence in Moscow during next week's Champions League final after the clashes in Manchester this week, but is doing all it can to prevent it, Russia's ambassador to London said on Friday.

A Russian fan was stabbed in the back before Russian team Zenit St Petersburg's 2-0 win over Rangers in the UEFA Cup final in Manchester on Wednesday.

Nearly 50,000 English fans are expected to flock to Moscow for the showdown between Chelsea and Manchester United.

"There are some concerns but we hope that the Russian authorities, in close cooperation with the relevant British authorities, will try to maintain law and order," Ambassador Yuri Fedotov told Reuters in an interview.

"I hope everything will go well and that people will be able to avoid such clashes as happened ... in Manchester," he said.

Fighting between Scottish fans and riot police in the centre of Manchester later left 15 police officers injured and led to 42 arrests.

Fedotov said Russian Sports Minister Vitaly Mutko had pledged the authorities would take all necessary measures to maintain law and order during the Champions League final.

He did not think there was a risk of retaliation against English fans in Moscow for the stabbing of the Russian fan in Manchester.

"First of all its an all-English final. No Russian fans are involved. Secondly the capacity of Luzhniki (stadium) is such that if 50,000 English fans take their seats in the stadium there will be very little (space) for the Russian fans, although there are fans of both Manchester United and Chelsea in Moscow," he said.

He urged English fans to behave responsibly and take the match in a positive spirit.

"After all, it's an all-English final and not withstanding who will win, it will be an English team who will get this Champions League cup," he said.

Moscow's relations with Britain have been strained since the November 2006 poisoning in London of ex-KGB agent Alexander Litvinenko.

In what Fedotov called a goodwill gesture, Russia has waived visa requirements to allow thousands of English fans to attend the final. A valid match ticket will act as a visa to enter and leave Russia between May 17 and 25.

However, Fedotov said some English fans would arrive in Moscow without match tickets.

"We (the Russian embassy in London) have issued already about 3,000 visas to fans who are going to Moscow with no tickets. They hope to buy tickets in Moscow or they hope to watch the football somewhere in ... pubs or clubs," he said.

(Editing by Justin Palmer)