"I think even when Luis does get blatant penalties now he doesn't get them," said Gerrard.
"It is down to referees to not judge him and give what they see - if it's not a penalty don't give him one but if it's clear give it.
"He was booked at Sunderland but against United it was a penalty."
Johnson echoed the sentiments of his captain by adding: "Everyone has to do their job: they have to forget about who they are looking at and make their decisions and not let anything from the past affect their decision.
"They have to call the shots at the time, regardless of who it is."