Leeds made an offer of €18m for the Brazilian striker in mid-August, but Basel are asking for €20m.
The English club want to pay an initial €15m and a further €3m in performance-related bonuses.
Paulo Pitombeira and Luiz Portela, who represent Cabral, 22, are in Portugal to try and speed up a sale.
He wants to play in the Premier League but the two clubs must agree terms to make it possible.
Centre-forward Cabral scored 14 goals in the 2019-20 Swiss Super League, his first season in Europe.