"Liverpool" coach Brendan Rodgers and captain Steven Gerrard urge referees not to have a preconceived opinion about Luis Suarez.
The 25-year-old Uruguayan has gained a reputation as a diver, which harms the whole team.
"I think even then, when a penalty for diving against Suarez should actually be given, the referee hesitates to do so," said Gerrard. "But the referee must not have a preconceived bias and make a decision that he believes is right at that time. Against 'Man Utd', he should have earned a penalty."
Rodgers added: "In modern football, there is no shortage of players who end up on the ground when they shouldn't. But sometimes they get away with it. Last week Suarez was brought down after contact, but received a warning. Against 'Man Utd', a penalty was once again not awarded."