The Belgian international was at Goodison Park on Sunday to watch Lampard’s side fall to a tight defeat at the hands of Chelsea, who needed a Jorginho penalty to get their Premier League campaign off to a winning start.
That has been something of a theme in east London this summer, as even despite the big-money signings of Nayef Aguerd and Gianluca Scamacca, David Moyes has watched another target in Jesse Lingard move elsewhere.
West Ham will meet Lingard next week when Nottingham Forest visit the London Stadium, while a potential clash against Onana could come in September when Moyes’ side travel to Merseyside.
“I am a big fan, that is why he is coming,” said Lampard to Sky Sports on Saturday.
"When you come in as a manager you want to influence the style of the team and he is a young player that has, for me, everything in terms of physicality, quality on the ball and defensive mindset, an all-rounder for us.
"He is going to have a big impact on the club and is a good lad with real confidence about him. I don’t want to hang too much on him, but I am very pleased he is coming in."