Mauricio Pochettino says the decision to leave his role as boss of the USA national team to become Manchester United head coach was "one of the most difficult" of his career.
The Argentine was announced as Michael Carrick's successor at Old Trafford on Friday, with sources telling BBC Sport he has signed a two-and-a-half-year contract.
United paid a release clause in the region of £7.4m to extract Pochettino from his USA contract, with a further payment being made for his backroom staff.
Pochettino only signed a new four-year deal with the USA in the summer, but will depart for Manchester after leading the national team in matches against Haiti on 14 and 18 November.
The 54-year-old broke down in tears during his first news conference after his move to United was confirmed, and thanked the US Soccer Federation for its support.
"It's difficult to talk now," he said. "I'm a very emotional guy. It's a very sad decision.
"But we are professionals and we are trying to make our dreams come true."
Asked why he signed a new deal with the national side only to accept United's offer, Pochettino said the chance to manage at Old Trafford was too good to reject.
"I never said I wanted to go back but they know there aren't too many opportunities that happen…
