LONDON (Reuters) - Some clubs have expressed concern about the viability of a new European competition, known as Europa League 2, which will start in 2021, the head of the European Leagues umbrella group said on Friday.

The European Leagues, which represents the continent's national leagues, hosted a meeting in London on Thursday which it said featured 201 clubs to discuss the future of UEFA competitions.

One change that has already been decided is that the second-tier Europa League competition will be reduced in size from 48 teams in the group stage to 32 starting from 2021, while the Europa League 2 tournament will be introduced, also with 32 teams in the group stage.

However, European Leagues chairman Lars-Christer Olsson said some clubs were worried about the potential success of the third competition.

"Clubs say there is a risk that if the matches are not important enough, then they cannot fill stadiums or generate incomes," European Leagues chairman Lars-Christer Olsson told reporters. "So if we introduce a third competition where clubs are losing money, then it will be counter-productive."

"We have said all along that we acknowledge and think it is fine to introduce a third level of competition," he added. "It was only yesterday that the clubs said they had concerns, so we have to check whether they think they are right or not."

Olsson reiterated that the European Leagues were opposed to any change in the format of UEFA competitions which would involve teams playing more European matches at the expense of domestic ones.

This could put it on a collision course with the European Club Association (ECA), headed by Juventus president Andrea Agnelli, which says it wants more European matches for more clubs.

"We are of the opinion that there is no room in the calendar for any more matches and we are not in favour of reducing the number of teams in the domestic competitions," said Olsson.

"We think the decision on how the leagues should be structured is a domestic matter... it is not something which should be decided by an international body," he said. "So we think the number of matches are okay as they are today."

(Writing by Brian Homewood in Zurich; Editing by Toby Davis)