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 in your career like Manchester United," he said. "When it arrives, it's difficult to turn down."

Carrick was sacked on Thursday after United's worst start to a domestic campaign in 40 years, which has left them languishing in 18th place in the Premier League.

Pochettino will inherit a side that have won just once in 10 league matches this season and sit just one point above bottom-placed Sunderland.

His first match in charge will be an away match against Liverpool on 22 November.

A decade in the making

Pochettino's arrival at Old Trafford marks the end of a decade-long courtship.

Thriving during an 18-month stint at Southampton, he led the Saints to eighth place during his only full season on the south coast.

Tottenham moved quickly to appoint one of the most promising young coaches in Europe in 2014, and it was in north London that his reputation rocketed.

The club had finished in the top four just twice in the 22 years before his appointment, but Pochettino led them there four times in his five full seasons.

It was two years into his time in the capital that United first considered a move for Pochettino.

The Argentine dined with legendary former United boss Sir Alex Ferguson in Mayfair, London just weeks before Louis van Gaal was sacked as Red Devils boss.

The club ultimately decided to appoint Jose Mourinho, and Pochettino was again overlooked when the Portuguese departed in 2018, with Ole Gunnar Solskjaer impressing so much in an interim role that he was given the job more permanently.

In 2022, it was between Pochettino and Erik ten Hag for the United job but the board opted for the Dutchman, who had led Ajax to the semi-finals of the Champions League in 2019, when they were beaten by Pochettino's Tottenham.

Pochettino was interviewed by United again in 2024 following his exit from Chelsea, but the board opted instead to hire Ruben Amorim from Sporting to replace Ten Hag.

Carrick 'incredibly grateful' despite exit

Shortly after Pochettino's appointment, Carrick released a statement on social media thanking United's fans for their support during his time in charge of the club.

"Dear United fans, I've had the immense privilege of leading Manchester United, the football club that I love," wrote Carrick.

"There are very few who get to live that and feel it, and for that I'm incredibly grateful.

"With that comes huge responsibility, and to be at Manchester United, you need to understand exactly what that means.

"It's different to anywhere else."

In a wide-ranging post, Carrick, who signed a two-year deal with the club in May, said the club's culture and values drove him at Old Trafford.

"Ultimately, you need to push to be the best, but there is a culture, there are values and there are behaviours that you have to live by and respect, which have been built over a long period of time," he wrote.

"It's a football club that is unique, with substance and history that cannot be ignored.

"This is what inspired me every single day."

United board unanimous about hiring Pochettino

Manchester United have made it pretty clear Mauricio Pochettino is the only coach they spoke to directly about taking over at Old Trafford.

Eddie Howe, Julian Nagelsmann and Antonio Conte were also mentioned as possibles in the aftermath of that awful 3-0 home defeat by Bournemouth three weeks ago, but evidently Pochettino emerged as the first choice.

Interestingly, United have felt it necessary to state privately any claim of a split between the Glazer family and Sir Jim Ratcliffe is "categorically false" in their words.

I reported earlier this week a mechanism by which the Glazer family could take back control of the football operation from Ratcliffe.

There has been no Stock Exchange statement that has happened - there was one that Ratcliffe had been handed control by the board when he agreed to buy into United in December 2023.

There has been huge criticism by fans of the way United are being run. Sporting director Jason Wilcox is blamed by many for bad recruitment, but the budget was set higher up.

United officials are keen to stress unanimity in the hierarchy but with the club 18th in the Premier League and having sacked three managers in three seasons, none of the owners can be happy. It is one to keep an eye on.