David de Gea left Manchester United last summer after the expiration of his deal at the club and Erik ten Hag splashed the cash to sign Onana.
The goalkeeper has been guilty of making a number of mistakes and the microscope has been placed firmly on his performances.
Manchester United will be looking for Onana to perform well at Liverpool this afternoon, but Mellor is not convinced by the shot-stopper.
Mellor insists that there is now a major lack of trust in Onana and he is not at Alisson’s level as a goalkeeper.
“He’s had a tough start because he’s made so many mistakes; he’s not just made the odd mistake, he’s made a lot of mistakes”, Mellor said on LFC TV.
“We talk about confidence, trust in the goalkeeper, which we have with Alisson.
“I don’t think the United fans have trust in Onana. I’m not convinced the defence in front of him does because they are thinking ‘is he going to make another mistake?’.
“You have to remember, he has taken over from David de Gea; he got the golden glove in the Premier League last season, so big gloves to fill.
“He’s obviously a decent goalkeeper, but he’s nowhere near as good as Alisson.”
Onana, 27, has so far managed to keep five clean sheets for Manchester United in the Premier League, while in the club’s recently concluded Champions League campaign he conceded 15 goals in just six games.
