The Argentina centre-half has been added to incoming Red Devils boss Ten Hag's wish list.
The 24-year-old moved from Argentina club football to join the Dutch giants in 2019 and has helped win two Eredivisie titles.
Martinez is adept at playing out from the back and suited to Ten Hag's 'one-v-one defensive tactic'.
The six-cap star has three seasons left on his Ajax deal and is valued at about £25million.
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