The 29-year-old is reportedly earning wages in excess of £500,000 a week following his high-profile switch from Premier League rivals Arsenal in January.
Sanchez’s United career has yet to take off, though, as he has scored just one goal in 10 appearances and was overlooked for selection in the 2-0 win over Brighton & Hove Albion last weekend.
A number of former players have hit out at the Chile international for his level of performances, while a report in the British press on Wednesday suggested that United officials are growing concerned by his early form.
Speaking to reporters upon linking up with his Chile teammates in Sweden, Sanchez admitted that he has found life tough since joining the Red Devils.
“As I am self-demanding, I expected something better,” he said. “After my arrival at United, it was hard to change everything very quickly. I even hesitated to come here [to Sweden].
“I had asked permission to miss these games, but then I thought better and spoke with Claudio [Bravo] and told him that we should all be united.
“The change of club was something that was very abrupt – it was the first time I’ve changed clubs in January – but many things have happened in my life that are difficult.”
Sanchez is a part of the Chile squad for the friendlies against Sweden and Denmark over the next six days.