This includes the Chilean's now-famous dogs Atom and Humber, who were hugely adored by the Arsenal faithful and will now be warmly embraced by Red Devils fans.
Much was made of Sanchez's signing video, but as well as the forward appearing in a Manchester United kit with number seven on the back, his dogs also appeared on social media sporting brand new personalised jerseys.
Atom and Humber
The most famous dogs in football, Sanchez's pets Atom and Humber even have their own Instagram account. The Manchester United forward regularly shares snaps of his pooches on his own Instagram page, but set up a second special social media profile just for cute photos of his pets.
During his time at Arsenal, Sanchez regularly was seen with his two dogs, who gained their own following among Gunners supporters. Arsenal fans even created a banner for Atom and Humber that was hung at the Emirates until the Chile international left for Premier League rivals United.
"Atom is one of the characters in a movie called Real Steel," Sanchez told Arsenal's official website in 2016.
"Atom the robot is very old and apparently useless but when he starts fighting he beats the best robots in the world.
"I like the movie so much that I thought I would call my first dog Atom. My other dog Humber reminds me of my brother Humberto. My brother is a very sweet guy, just like Humber is."
Sanchez also revealed that the dogs are not just popular in England, but are famous back in his home country after appearing in an advertising campaign for a dog food company.
"I just had the idea of creating an Instagram account for them so people could follow what they do," he continued. "The thing is both became famous in Chile after starring in Master Dog’s advert.
"I upload videos or pictures to their accounts whenever I can and I even saw their pictures on billboards when I went to Chile. They were smiling for the advert: what great acting! It really made me laugh."
Some fans are unsure which dog is which, but it is easy to tell the difference as Atom is a darker colour than Humber.
Sanchez is not the only famous footballer to have a canine companion, with many of the world's top names owning dogs. Lionel Messi received a present of a mastiff puppy from wife Antonella, and within a few months, the massive animal had grown into its name - Senor Hulk!
Harry Kane's pair of labradors are named after two of his favourite American Football stars Tom Brady and Russell Wilson, while Mesut Ozil's pug takes his name from the Rocky films. Neymar's dog Poker was given his unusual moniker by his card-game loving owner.
The ever-eccentric Mario Balotelli adopted two dogs from a rescue centre while at Liverpool, and even brought them to training with him. Initially, reports indicated that the pair of Staffordshire bull terriers were called Stevie and G after Reds captain Steven Gerrard, but they actually were given clever names from the Super Mario videogame - Luigi and Bowser!
|Mario Balotelli||Luigi & Bowser||Staffordshire Bull Terriers|
|David de Gea||Maxto||Chow Chow|
|Memphis Depay||Simba||Chow Chow|
|Harry Kane||Brady & Wilson||Labradors|
|Lionel Messi||Senor Hulk||Mastiff|
|Alexis Sanchez||Atom & Humber||Golden Retrievers|
|Chris Smalling||Miley||Cocker Spaniel/Jack Russell Cross|
As well as players owning dogs, they are also a big part of football in general, with many teams having dogs as their official mascots. Many of these even have official Twitter accounts, with thousands of followers. Blackburn's Rover the Dog uses his Twitter account to keep fans updated of charitable events and post photos of fan events.
Barnsley's Toby the Tyke got into a spot of bother in 2003 after throwing sweets into the crowd during a game, with one fan lodging a complaint after a sweet hit a young girl in the eye. The incident caused the mascot's actor David Betts to resign from his position after spending seven years putting on the dog suit for Barnsley games.
During the 1990s, Spanish football's governing body Liga Profesional de Futbol (LFP) used a dog called Goti as their mascot before replacing him with a more modern logo. The 1994 World Cup in the United States had a dog as its official mascot - one which bore the cumbersome title "Striker, the World Cup pup".
Before the men-in-suits mascots of today's football, teams actually used real live animals as lucky charms before games. This is still continued in some parts of the world, with Chilean side Colo Colo (a former team of Alexis Sanchez) bringing out rescue dogs with the players before games in order to help them find forever homes.
|Blackburn Rovers||Rover the Dog|
|Celtic||Hoppy the Hound|
|Doncaster Rovers||Donny Dog|
|Huddersfield Town||Terry the Terrier|
|Montreal Impact||Tac-Tik the Dog|
|Port Vale||Boomer the Dog|