Sanchez joined Manchester United in a stunning January deal from Arsenal last week.
He swapped places with Henrikh Mkhitaryan and signed a £500,000 a week deal.
Sanchez made his debut last week and already impressed in training, and Sanchez has branded the move amazing.
“I still find it hard to believe it’s actually happened. It’s amazing,” he said.
“A player of his stature and calibre has obviously come from a big club like Arsenal and then to move to a massive club like Manchester United, that for me makes me proud to be a Manchester United player because we want great players and exciting players.
“Its great to see him wear a United shirt and I’m sure he’s going to be successful.”
Sanchez’s move to United was a shock after Manchester City had tracked him for months.
He had agreed a move to City but was so desperate to leave Arsenal opted to sign for United when City backed out of a deal for this month.
United were ready to pay over the odds in agent fees and wages to land their man and handed him Beckham’s old No 7 shirt.
Beckham was today granted permission to finally launch his MLS franchise in Miami.
He appeared in front an audience to announce the club – although a lot of the details are still to be made public.
But he was still ready to talk about his old club and thinks Jose Mourinho’s new deal at Manchester United is a good move.
“Of course he’s the right fit for Manchester United,” Beckham said. “We’re talking about Jose Mourinho. He’s one of the best managers in the game.
“Manchester United has had success over the last 25 years because we have had stability that has run throughout our club.
“Sir Alex Ferguson – the amount of time he was manager of the team – that’s why we were successful because we had stability that ran through the club and that’s what we need going forward.
“Everyone is going to have their own opinion of (Mourinho) as a manager, him as a person, him as an individual. But is he the right person to lead Manchester United? Yes, of course he is.”
