Ajax chief Marc Overmars and United's Scandinavian scout Tommy Moller Nielsen both saw Sulemana score on Monday night against FC Copenhagen.
Ajax are willing to pay €10m for the 19 year-old Ghana international, while United are willing to go closer to €20m.
And Dutch reporter Mike Verweij said on the De Telegraaf podcast: "If you see that Donny van de Beek, who was simply one of the best players in the Eredivisie, is not yet successful at Manchester United, then I think it is very unwise for Sulemana to go in that direction.
“But it will drive up the price. And whether Ajax is able to lay down a lot for him in this time of corona ... That will be very difficult. The price we initially heard was six, seven million. But when you hear that United might be willing to pay twenty million euros for him ... That seems very strong for a guy who has not yet proven himself very much in Denmark. But I also don't know what Ajax can pay. It will be a dime on its side, I think."
Meanwhile, Ajax coach Erik ten Hag said: "He is an attractive player who is technically skilled and goes on an adventure and has a lot of speed. We now have to see if we can make his arrival concrete."