The 20-year-old is a product of the famed La Masia academy system at Camp Nou, having spent five years in Catalonia.
He was allowed to depart in January 2015, as Ajax moved to take him to Holland.
Onana has developed at an impressive rate with the Eredivisie giants, earning regular first-team recognition.
It is now being suggested that his future lies outside of Amsterdam, and the Cameroon international is refusing to close the door on a possible return to Barca.
He told Marca: "I would love to come back because La Liga is one of the best leagues in the world.
"We'll see if I return to Barcelona.
"If I leave Ajax, it'll be to join an even bigger club.
"You have to do everything right here before going back, but I'd like to return."
Onana admits to enjoying his time with Barca, but insists he has no regrets at having moved on once it became clear that his route to the senior side was blocked – with a man now on the books at Manchester City edging him down the pecking order.
He added: "I have a lot of beautiful memories of my time at La Masia, but I had to leave to grow as a footballer.
"It was a decision I had to make.
"They had just signed Claudio Bravo and it wasn't clear whether I'd get a chance so I left - had I stayed everything would have been more difficult."