The League Managers Association has expressed concern that additional assistant referees employed in Europa League group games appeared to be nothing more than silent partners, reports The Guardian. "The LMA initiated the study as it places great importance on technical issues within the game," said the chief executive Richard Bevan. "The LMA and other relevant bodies are convinced that goal-line technology is crucial for the development of the game but are also supportive of this type of experiment, in that it should lead to improved decision making by officials.

"Football has changed and developed enormously over recent years and the job of the referee has become increasingly difficult."

The LMA sought the opinions of, among others, the Everton manager David Moyes, the Fulham manager Roy Hodgson and Celtic's Tony Mowbray, and received mixed reviews.

In publishing their findings, the LMA stated: "The additional assistant referee [AAR] appears reluctant to get involved and seems to be dominated by the referee, and at times by the assistant referee, even when the AAR has the best view.

"The AAR is a top-level official and his abilities appeared not to be used to the fullest potential in this initial experiment. They should be encouraged to contribute more to the decision-making.

"We would like to see additional trials involving a greater sample of games and there should also be trialling of goal-line technology and video replays. AARs should not be seen as an alternative to the use of technology."

The LMA will now present its findings to football's governing bodies, including Fifa and Uefa.