By Nick Teale
 
Arsène Wenger has called on UEFA to explain how they appoint and assess referees for games in their competitions.
 
The manager is keen to understand how European football's governing body ranks the officials it appoints to fixtures. The call comes after criticism of certain referees' performances during this week's Champions League matches.
 
Wenger was unimpressed with Martin Hansson's performance in Porto on Wednesday night, while Norwegian official Tom Henning Ovrebo received criticism for some of his decisions in Bayern Munich's 2-1 win over Fiorentina on the same evening.
 
"It has to be clarified first of all how they nominate referees for games," said Wenger.
 
"They have to be much more open on how they rate their referees. Nobody knows really how they name their referees.

"Where is the ranking of the referees? I believe there is too much gone on in the last 30 years. I do not want to say more on that. There are a lot of things that have to be done."

Copyright 2014 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source 19 Feb 2010