Pochettino is the favourite to take over from interim boss Ralf Rangnick in June, providing the Argentine can cut short his contract with Paris Saint-Germain.
But Sportsmail understands United will turn to Ajax coach Ten Hag if the club are unsuccessful in their attempt to appoint Pochettino.
Erik ten Hag is the alternative target for Man United if they cannot get Mauricio Pochettino
Ten Hag is said to be interested in the United job and Ajax would not stand in his way if he wants to leave at the end of the season, even though the 51-year-old is under contract in Amsterdam until 2023.
The two clubs enjoy a good relationship and Ajax chief executive Edwin van der Sar, the former United goalkeeper, played a key role in Donny van de Beek’s £40million move to Old Trafford.
Ten Hag is viewed as one of the most progressive coaches in Europe and was approached by Tottenham to replace Jose Mourinho before signing a contract extension with Ajax in April.
Rangnick, 63, is poised to be confirmed as United’s boss until the end of the season, when he will hand over to a permanent successor and take up a consultancy role.
United reached an agreement this week with Lokomotiv Moscow for Rangnick, the Russian club’s head of sports and development.