Roberto Mancini believes that referees are likely to make mistakes as they become more weary throughout the season.
The Manchester City manager blasted match official Phil Dowd for giving a controversial penalty against the Premier League leaders during their Carling Cup semi-final defeat to Liverpool on Wednesday.
"I think playing a lot of games is also difficult for [referees]," said Mancini. "The refs sometimes are tired - to play every two or three days is difficult for the players, and for the referee.
"The referee is like me, like the players. They can be tired sometimes."
City have a break from action this weekend following their FA Cup defeat to Manchester United earlier this month, but will resume Premier League focus for their match against Everton on Tuesday.