Ajax are claimed to value the 24-year-old at £43m. Both Arsenal and United have offered the same amount, but the Red Devils have guaranteed more up front.
Martinez has been respectful to Ajax so far but is keen for at least one of the bids to be accepted. The versatile star can play in central defence, left back and in defensive midfield.
He joined Ajax from Argentine club Defensa y Justicia in 2019 and has been a regular since, making 120 appearances in all competitions. Arsenal have focused their attention on other areas of the pitch so far in the window but Martinez is their top defensive target.