The Chile international sealed his switch to Old Trafford on Monday in a massive swap deal that sees Henrikh Mkhitaryan move to his former club Arsenal.

Sanchez's move ends months of speculation as his contract at Arsenal wound down well into its final year and comes after Premier League leaders Manchester City had heavily pursued his signature since the previous transfer window.

After arriving at United, the 29-year-old was thankful to the Gunners, with whom he spent three-and-a-half years having signed from Barcelona, but felt the chance to play for the 13-time Premier League winner was simply too good to turn down.

"I am thrilled to be joining the biggest club in the world," the forward said.

"I have spent three-and-a-half wonderful years at Arsenal and I bring with me very positive memories of that great club and its fans. 

"The chance to play in this historic stadium and to work with Jose Mourinho was something I could not turn down. 

"I am very proud to be the first Chilean player ever to play for United's first team and I hope I can show our fans all around the world why the club wanted to bring me here."

United boss Jose Mourinho, meanwhile, was delighted with his latest star acquisition and also wished Mkhitaryan well.

"Alexis is one of the best attacking players in the world and he will complete our very young and talented group of attacking players," said Mourinho.

"He will bring his ambition, drive and personality, qualities that make a Manchester United player and a player that makes the team stronger and the supporters proud of their club dimension and prestige.

"I would like to wish Henrikh all the success and happiness that I am sure he is going to get. He is a player that we will not forget, especially for his contribution to our Europa League victory."