Markus Merk will take charge of the first leg of Chelsea's Champions League semi-final against Liverpool on Wednesday. The German, a dentist by trade, has established himself as one of the best referees in Europe and featured at the 2006 World Cup.

Merk will be in the spotlight as Jose Mourinho has accused referees of favouring other clubs following a weekend where they were denied a penalty at Newcastle with the Chelsea boss claiming it was "forbidden" to award penalties against Manchester United.

The game is a repeat of the last-four clash in 2005 which ended in controversy when referee Lubos Michel allowed Luis Garcia's second-leg winner to stand, although TV replays could not prove the ball went over the line.