The new Premier League season is less than a month away and clubs are busy building their squads before the end of the summer transfer window.
Manchester United were expected to be busy in the market, but have so far only added the £60 million signing of Matheus Cunha to their ranks.
However, after a disappointing season last year, Ruben Amorim will be keen to add further new recruits.
"Top sides always have a top goalkeeper that they are assured with, and Onana is not that goalkeeper.
"I can’t see how he’s going to cover up what he did last season, and I just really don’t believe that he can. If I don’t believe as someone watching, I worry what the players in the team are thinking. If you don’t believe in your goalkeeper and you’ve got that fear factor, it will cost you.
"I question if he was born a goalkeeper. I think he was an outfield player that has gone in goal. He wasn’t a goalkeeper from day one.
"The only thing he really hasn’t done, is become a goalkeeper. I don’t care what he did at Ajax or Inter; he’s not good enough to play at Manchester United."

Ahead of his first full season in charge, Amorim is looking to shape the United squad in his own style, with reports he favours 'shot-stopping' over goalies who are better with their feet, which could lead to a change between the sticks for the Red Devils.
However, Parker slammed his old club for making a mistake and getting rid of David de Gea because of his perceived lack of ability on the ball.
Adding, "United got rid of David De Gea because his feet weren’t good enough.
"If De Gea had been their last year, United would have at the worst been sat comfortably in the mid-table, the amount of saves De Gea made.
"To be honest, they sh*t on De Gea, United fans. Three player of the seasons at United, player of the season at Fiorentina, that says everything.
"Everyone got caught up in this stupid thing that football people pushed out there about keepers being good with their feet, and football fans fell for it."