The Gunners are reportedly close to agreeing on a deal for the former Barcelona academy star.
The former Barcelona academy star was handed a 12-month ban for a doping case as a banned substance called furosemide was found in his urine sample last October.
Onana has appealed to CAS for the allegation, and the Gunners are said to be looking forward to the hearing, which will be held on Wednesday.
The 25-year-old’s contract expires next year, with Ajax director Marc Overmars believing that the shot-stopper won’t extend his deal.
Overmars said: “We have not stopped the negotiations for nothing. I think it is likely that he will leave in the summer. “
It is also reported that Ajax would demand around £8m if Onana’s ban gets lifted. Still, they could settle for about £2m transfer fee should the opposite happen, as the Eredivisie champions want to avoid him leaving on a free transfer next summer.
Onana could be the first major signing of the North Londoners, who are seeking a replacement for Bernd Leno.
Mikel Arteta is said to be unhappy over the German keeper’s liabilities between the sticks. Gunners are looking to amend the situation after the recently concluded season.
Instead, the Spanish manager wants a shot-stopper who excels at distribution, especially when playing out from the back, and Onana looks a perfect fit.
The Cameroonian international is a tailor-made option for Arteta’s style of play, thanks to his upbringing in a club like Barca and later Ajax.
Onana has developed into one of Europe’s promising goalkeepers after establishing himself as one of the best young keepers at Ajax over the past few seasons.